Questions 1 - Oxygen and the oxides

Q1. In each of the processes, state whether carbon dioxide in the atmosphere increases, decreases or stays the same:

i. burning fossil fuel
ii. volcanic activity
iii. dissolving in oceans

Answer
Q1 i. Increases
ii. Increases
iii. Decreases - although the overall CO2 level in the world doesn't change, it is taken from the air into the ocean. Read the question!

Q2. The pie chart shows the composition of air today. Choose the correct option:

Gas x is:

a. chlorine

b. hydrogen

c. nitrogen

d. radon

Answer

Q2. Gas x is nitrogen. 

If you don't know this by heart, you can take an educated guess: 

- Chlorine is poisonous (so that can't be)

- Radon is radioactive (so that can't be either)

You're left with 2 options, nitrogen or hydrogen. Each gives you a 50% chance of getting the mark. So hopefully, you'd have ticked/crossed nitrogen :)

1.40 Explain, using dot and cross diagrams, the formation of covalent compounds by electron sharing for the following substances...

Here are dot and cross diagrams to represent the covalent bonds between the following substances:

• Hydrogen
• Chlorine
• Hydrogen chloride
• Water
• Methane
• Ammonia
• Oxygen
• Nitrogen
• Carbon dioxide
• Ethane
• Ethene

This website covers hydrogen, chlorine, hydrogen chloride, water, methane ammonia, and oxygen.

The rest can be found here (quizlet) or click on the "Formulas 1.40" page on the right side ^_^

4.21 Explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.

Already mentioned in 4.20

It speeds up a reaction by providing an alternate pathway, so lower activation energy is required.

4.20 Explain the effects of changes in surface area of a solid, concentration of solutions, pressure of gases and temperature on the rate of a reaction in terms of particle collision theory

Surface area
There is more surface that is in contact, so it's more likely that there will be successful collisions that lead to a reaction >> faster rate of reaction

Concentration/Pressure
There's more particles so, again, it's more likely that there will be successful collisions that lead to a reaction >> faster rate of reaction

Temperature
Particles are moving faster, so they collide more frequently. Because of this, there is going to be more successful collisions, which increases the rate of reaction

Catalysts
Catalysts make the reaction require less activation energy, providing an alternate "route" for the reaction

4.19 Understand the term activation energy and represent it on a reaction profile

The activation energy is the minimum amount of energy required for a reaction to occur.

This is a reaction profile:

4.18 Describe the effects of changes in surface area of a solid, concentration of solutions, pressure of gases, temperature and the use of a catalyst on the rate of a reaction

• The more concentrated, the faster the rate of reaction
• The larger the surface area, the faster the rate of reaction
• The higher the temperature, the faster the rate of reaction
• The higher the pressure, the faster the rate of reaction
• Use of a catalyst also increases the rate of reaction. The more there is of the catalyst, the faster the reaction.

4.17 Describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction

Surface area

• Put a certain mass of a metal, let's say magnesium, into a beaker with x amount of sulphuric acid in it (let's say 100ml). Do this with a block of it.
• Time the reaction, record results
• Repeat step 1 but use another form (i.e. powder)
• Time the reaction again, record results
• Keep repeating with different forms (i.e. strips, etc.), making sure to always use the same mass of the same metal with the same amount of sulphuric acid.
• You should see that the powder will have the quickest reaction because it has the largest surface area.

Concentration

• Put a conical flask on a mini whiteboard on a table. Draw an x in the middle of the whiteboard. Place the conical flask on top
• Presume that 0.2g of sulphur is produced
• Keep changing the ratio of sodium thiosulfate and water, always adding the same amount of hydrochloric acid and measure how long it takes for the cross to be obscured
• Repeat as required
• From this, calculate the concentration (moles ÷ volume = concentration)

Figure 1: My sad looking drawing of the experiment, but I hope you can tell what I mean

Temperature

• Put x amount of magnesium into y amount of sulphuric acid at room temperature
• Time reaction, record results
• Repeat at different temperatures
• You will see that the greater the temp, the faster the rate of reaction

Use of a catalyst

• Put x amount of hydrogen peroxide into a conical flask with y amount of manganese dioxide
• Time how long it takes for the oxygen to displace all the water in the gas jar
• Repeat, increasing the amount of manganese dioxide each time. Yes, you still have to time the reaction. Keep amount x (of hydrogen peroxide) the same
• You will see that the more catalyst you have, the faster the rate of reaction

Figure 2: My second sad looking diagram...I hope you still have some idea of what I mean...

4.9 Describe experiments to carry out acid-alkali titrations

Ignore the flea in the diagram above (not sure what it is....)

• Prepare the apparatus above
• Fill the burette with a known volume of acid (eg 100cm3)
• Fill the conical flask with a known volume of alkali
• Put an indicator in the conical flask (let's say you're using phenolphthalein) 
• Using the tap, slowly drip the acid into the alkali, stirring every 10 seconds and watching carefully for the phenolphthalein to turn colorless (it's pink in alkalis) - this will mean that it's neutral. At this point, stop pouring in the acid immediately.
• Once it has turned colorless, see how much acid you've used up
• Repeat the process using the known volume of acid into the known volume of alkali without the indicator. 
• Your solution is now neutral and not contaminated with indicator :) (If you did it right, which hopefully you did)

4.8 Describe experiments to prepare insoluble salts using precipitation reactions

• Mix two solutions together (let's say silver nitrate and sodium chloride)
• A product will form
• Filter the mixture
• Collect solid from filter paper
• Wash with water
• Leave to dry in an oven or do so between bits of filter paper

A good way to remember this is

MFWCD

My

Friend's

Weirdly

Colored

Duck

or, if you prefer,

My

Friend's

Wacky

CD

Sums up this:

Mix

Filter

Wash

Crystallize

Dry

4.7 Describe experiments to prepare soluble salts from acids

You could do the following:

• Add an excess of sulphuric acid to a metal (let's say zinc) 
• Watch it react
• Filter off the excess zinc
• Heat the solution gently for about 2 minutes
• Put aside, leave to cool until crystals form
• Dry between bits of filter paper

Sulphuric acid + zinc → Zinc sulphate + hydrogen

This is what zinc sulphate looks like :)

4.6 Understand the general rules for predicting the solubility of salts in water:

• All common sodium, potassium and ammonium salts are soluble
• All nitrates are soluble
• Group 1 metal salts are soluble
• Common chlorides are soluble, except silver and lead(II) chlorides
• Common sulphates are soluble, except calcium and barium sulphates
• Common carbonates are insoluble, except ammonium, potassium and sodium

If you want to test yourself, click here (don't worry, the link is to another page on this blog, I promise...it's a quizlet)

2.36 Understand the sacrificial protection of iron in terms of the reactivity series.

Sacrificial protection of iron means coating it with a layer of metal that is more reactive. This means that the reaction will take place with the metal that is more reactive rather than the iron itself. Sometimes, ships will use blocks of magnesium because electrons involved in the reaction will flow like a current to the more reactive metal.

2.35 Describe how the rusting of iron may be prevented by grease, oil, paint, plastic and galvanising

Anything that prevents air or water from coming in contact with the iron will stop or delay rusting. This is what grease, oil, paint and plastic does. Galvanising is putting a layer of zinc over the iron. This is also effective because, unlike iron, zinc doesn't rust.

2.34 Describe the conditions under which iron rusts

Water and oxygen cause iron to rust, forming hydrated iron (III) oxide. Okay well water isn't needed, but there's oxygen in water, which causes rusting.
Salty water can make iron rust faster because it is an electrolyte (a liquid containing ions which can conduct electricity). If it can conduct electricity it will allow the electrons to flow more easily, and hence speeding up electron loss (because we know that oxidisation can also be described as the loss of electrons)

Fig 1: Rusting over time

2.33 Understand the terms redox, oxidising agent, reducing agent

Redox: When a more reactive metal gains oxygen from the less reactive metal - the less reactive one is reduced and the more reactive one is oxidized. (aka a reaction in which both REDuction and OXidation occur)

Oxidizing agent:

Reducing agent:

 Thank you, Google :)

2.32 Understand oxidation and reduction as the addition and removal of oxygen respectively

Oxidisation is when something gains oxygen
Reduction is when something loses oxygen

(This is in terms of oxygen gain/loss)

OILRIG
(Oxidisation Is Loss - Reduction Is Gain)
This is in terms of electrons

Oxidation is when something gains ELECTRONS (use the dash in the acronym to remember, as electrons are negative - )

Reduction is when something loses ELECTRONS

2.31 Deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions

If a more reactive metal (A) is placed into a test tube (or other container) with a metal oxide (B) dissolved in water, it will displace that metal (B).

If a less reactive metal (C) is placed into the test tube with the metal oxide (B), no reaction will occur.

This applies to the solution of their salts as well. From this, you can see which is more reactive. I.e. if chlorine displaces bromine, you can tell that chlorine is more reactive. :)

2.30 Describe how reactions with water and dilute acids can be used to deduce the following order of reactivity: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper

Potassium, sodium, calcium and lithium all react with water, and very vigorously with acid. Calcium has a much less vigorous reaction.

Magnesium, zinc and iron react with acid and very slowly with water. 

Copper reacts with neither (boring!).

By watching their chemical reactions, we can put them into order of reactivity:

• Potassium
• Sodium
• Lithium
• Calcium
• Magnesium
• Zinc
• Iron
• Copper

Potassium + water ;)

2.39 Describe tests for the gases

Hydrogen
A lighted wooden splint goes pop when put into a test tube, for example, of hydrogen

Oxygen
A glowing splint will relight if placed into a test tube of oxygen

Carbon Dioxide
When bubbled into lime water (calcium hydroxide solution) the lime water will become cloudy white. A lighted wooden splint will go pop but as this happens in other gases it is an unsuitable test

Ammonia
It makes damp, red litmus paper turn blue. It has a characteristic choking, pungent smell and will put out a lit splint

Chlorine
It will turn damp blue litmus paper red; and moist indicator paper red. It then bleaches both papers till they are white. Like ammonia it has a sharp, choking odour and will also put out a lit splint

2.29 Understand that metals can be arranged in a reactivity series based on the reactions of the metals and their compounds: potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, copper, silver and gold

These metals, in order of reactivity are:

• Potassium
• Sodium
• Lithium 
• Calcium
• Magnesium
• Aluminium
• Zinc
• Iron
• Copper
• Silver
• Gold

4.5 Predict the products of reactions between dilute hydrochloric, nitric and sulfuric acids; and metals, metal oxides and metal carbonates (excluding the reactions between nitric acid and metals)

Metals

• METAL + ACID > SALT + HYDROGEN
• HOWEVER
• a metal only reacts with an acid if it is MORE reactive than hydrogen
• Metal + hydrochloric acid > metal chloride salt + hydrogen
• Metal + Sulphuric acid > metal sulphate + hydrogen
• You don't need to know
• metal + nitric acid

Metal oxides/hydroxides

• METAL OXIDE/HYDROXIDE + ACID > SALT + WATER
• the reaction will also heat up a bit
• Metal oxide/hydroxide + hydrochloric acid > metal chloride salt + water
• Metal oxide/hydroxide + nitric acid > metal nitrate salt + water
• Metal oxide/hydroxide + sulphuric acid > metal sulphate + water

Metal carbonates

• METAL (HYDROGEN) CARBONATE + ACID > SALT + WATER + CARBON DIOXIDE
• Reaction will fizz (as CO2 is being produced)
• Metal (hydrogen) carbonate + hydrochloric acid > metal chloride salt + water + carbon dioxide
• Metal (hydrogen) carbonate + nitric acid > metal nitrate salt + water + carbon dioxide
• Metal (hydrogen) carbonate + sulphuric acid > metal sulphate + water + carbon dioxide

2.28 Describe a physical test to show whether water is pure.

If the water boils at exactly 100 degrees celsius (212 degrees fahrenheit), it is pure.

2.27 Describe the use of anhydrous copper(II) sulfate in the chemical test for water (page 93)

Anhydrous means it has no water, and the initial color (because of this) is white. When water is added, it turns blue.

2.26 Describe the combustion of hydrogen

When hydrogen reacts with oxygen, there is a loud pop, a flame for a split second, and then it's all over. Hydrogen can be produced by reacting a metal with an acid, i.e. magnesium with sulphuric acid.

This reaction produces water...and energy, of course!

Hydrogen + oxygen → water

4.4 define acids as sources of hydrogen ions, H+, and alkalis as sources of hydroxide ions, OH ̄

This basically means that if something is acidic it contains positive hydrogen ions (H+), if it is alkali it contains negative hydrogen ions (OH-)

2.25 Describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron

Acid + Metal → Salt + hydrogen

All reactions involve bubbling as hydrogen is released.

Eg
Magnesium + sulphuric acid → magnesium sulphate + hydrogen

EXAM TIP: If it asks for a word equation, state the word equation - you're more likely to get the mark. If you do write a symbol equation, they won't mark it wrong as long as you get it completely correct.

4.3 Describe the use of universal indicator to measure the approximate pH value of a solution

    What is universal indicator?

      It is a mixture of a variety of other indicators and can be used to measure the approximate pH of a solution, however a more accurate value can be obtained using a pH probe

    

      When universal indicator is added to a solution it changes to a colour that shows the pH of the solution (using the ph scale)

o   STRONG ACIDS: red (0)

o   WEAK ACIDS: yellow (2)

o   NEUTRAL: green (7)

o   WEAK ALKALIS: blue light/dark (10-11)

o   STRONG ALKALIS: purple (14)

2.24 Understand that carbon dioxide is a greenhouse gas and may contribute to climate change.

Carbon dioxide, as mentioned above, is a greenhouse gas. This means it traps heat in the planet and stops the sun's rays being reflected away from the earth. Excess levels of carbon dioxide contribute to climate change, causing the earth to warm up at unnatural rates.

2.23 Explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density

• It's used in fire extinguishers because it's denser than air and deprives the flame of oxygen, making it die down.
• Carbon dioxide is dissolved into fizzy drinks at high pressure, so there's bubbles when you drink it :)

4.2 Understand how the pH scale, from 0–14, can be used to classify solutions as strongly acidic, weakly acidic, neutral, weakly alkaline or strongly alkaline

The ph scale is used to measure acidity and alkilinity

• Solutions with a pH less than 7 are acidic
• with 0 being a very strong (the strongest, really) acid
• and 6 (or as the number is closer to 7) being a very weak acid
• Solutions with a pH of 7 are neutral
• Solutions with a pH greater than 7 are alkaline
• where 8 (or as the number gets closer to 7) is a very weak alkali
• and 14 is a very strong (the strongest) alkali
•