Quantities of both reagents are given, which suggests that one reagent will be in excess and the other will be limiting. This is best considered in terms of the mole ratio:

2 moles of HCl will react with 1 mole of CaCO₃.

Therefore 0.20 moles of HCl will react with 0.10 moles of CaCO₃. 0.20 moles of CaCO₃ has been used, so the calcium carbonate is in excess, and the hydrochloric acid is therefore the limiting reagent.

2 moles of HCl will yield 1 mole of CO₂.

Therefore 0.20 moles of HCl will yield 0.10 moles of CO₂.

Thus Limiting reagent is HCl and maximum yield of CO₂ is 0.10 mol is the correct answer.

GeO₂ + 4HCl → GeCl₄ + 2H₂O is the balanced equation, so the total sum is 8 - don't forget that GeO₂ and GeCl₄ both have a '1' in front of them, although by convention we don't actually write that into the equation.

This question requires us first to work out the number of oxygen atoms in each formula, and to then multiply that by the number of moles, which will give us the number of moles of oxygen atoms:

0.05 mol Ca(NO₃)₂ : calcium nitrate has 6 oxygen atoms: 6 × 0.05 = 0.30

0.10 mol C₆H₄(NO₂)₂ : dinitrobenzene has 4 oxygen atoms: 4 × 0.10 = 0.40

0.20 mol CO : carbon monoxide has 1 oxygen atom: 1 × 0.20 = 0.20

0.10 mol O₂ : oxygen has 2 oxygen atom: 2 × 0.10 = 0.20

Thus 0.10 mol C₆H₄(NO₂)₂ is the correct answer as this contains the largest number of moles of oxygen atoms (0.40 mol).

A heterogeneous mixture is a mixture of more than one phase (or state) of matter. Hence Solid calcium carbonate powder suspended in water is the correct answer as this contains both a solid (calcium carbonate powder) and a liquid (water). The other answers are homogeneous (one phase of matter) mixtures (a solution like aqueous sodium chloride is uniform throughout and considered to be homogeneous), or in the case of nitrogen dioxide gas - a pure compound.

We need to find the simplest ratio of the number of (moles of) atoms. We cannot use a calculator so we will need to approximate the relative atomic masses that we take from the periodic table (e.g. carbon 12.01 = 12).

Start by assuming 100g: Thus 90g of C atoms, 10g of H atoms:

Therefore the empirical formula and the correct answer is C₃H₄

The ideal gas equation is PV=nRT. The letters represent Pressure, Volume, number of moles, gas constant (R) and Temperature in that order.

P against T and V against T will both give a directly proportional linear relationship as the two variables are on opposite sides of the equals sign in the equation; so any change in one variable must be proportionally mirrored in the other variable if all the other values are constant.

P against \({1\over V}\) will also give a straight line. If all other values in PV=nRT are constant then PV=constant. If we give that constant a value of 1 (PV=1) then P =\({1 \over V}\) so volume is inversely proportional to pressure and P against \({1\over V}\) will give a straight line when plotted.

P against V will give the curve (a hyperbola) as shown in the diagram since (in the same way as above) PV=constant, as pressure is increased volume decreases and vica versa. This inversely proportional relationship will (mathematically) always give a curve when plotted.

(If the maths is too much - learn the laws (Avogadro's, Boyle's, Charles' and Dalton's) on the revision slide.)

Thus P against V is the correct answer.

The mole ratio must be used to answer this question:

The reaction gives 2 moles of iron (Fe) for every 3 moles of carbon dioxide (CO₂) produced.

Therefore for every 1 mole of CO₂ produced, \({2 \over 3}\) of a mole of Fe is produced.

If 500 moles of CO₂ are produced, \({2 \over 3}\) × 500 = 333 moles of Fe will be produced.

Thus 333 mol is the correct answer.

C₂H₄ + 3O₂ → 2CO₂ + 2H₂O is the balanced equation, so the sum of the integer coefficients is 8 - don't forget that C₂H₄ does have a '1' in front of it, although by convention we don't actually write that into the equation.

(When balancing combustion reactions of hydrocarbons, first balance out carbon and hydrogen atoms by adding coefficients (numbers) in front of CO₂ and H₂O, after that balance the oxygen atoms and the hydrocarbon as required.)

The ideal gas equation is PV=nRT. The letters represent Pressure, Volume, number of moles, gas constant (R) and Temperature in that order.

If all other values in PV=nRT are constant then PV=constant. If we give that constant a value of 1 (PV=1) then P =\({1 \over V}\) so volume is inversely proportional to pressure (and P against \({1\over V}\) will give a straight line when plotted).

Therefore, if we halve the pressure, from 200 to 100 kPa, we must double the volume: Thus 200 cm³ is the correct answer.

Concentration (mol dm⁻³) = moles (mol) / volume of solution (dm³)

Moles (mol) = Mass (g) / molar mass (g mol⁻¹)

So moles of sodium hydroxide (NaOH) = 10.0/40.0 = 0.250

Concentration of the solution = 0.250 / 0.500 (The volume must be converted to dm³: 1 dm³ = 1000cm³)

Concentration = 0.250 / 0.500 = 0.500 mol dm⁻³

Ideal gases have a constant molar volume (at any given temperature and pressure).

Quantities of both reagents are given, which suggests that one reagent will be in excess and the other will be limiting. This is best considered in terms of the mole ratio:

1 mole of CH₄ will react with 2 moles of O₂.

So methane will react with twice its volume of oxygen (and vice versa, oxygen will react with half its volume of methane).

Methane gas is therefore in excess and oxygen is the limiting reagent.

The amount of methane that will react is therefore 500 cm³ / 2 = 250cm³ (1:2 ratio)

And 250 cm³ of methane reacting with give 250 cm³ of carbon dioxide (CO₂) (1:1 ratio)

Thus the answer is 250cm³

The mole ratio must be used to answer this question:

The reaction produces 4 moles of SO₂ for every 3 moles of CaSO₄ reacted.

Therefore for every 1 mole of SO₂ produced, \({3 \over 4}\) of a mole of CaSO₄ must be reacted.

Using Moles (mol) = mass (g) / molar mass (g mol⁻¹) (molar mass of SO₂ = 32 + 16×2 = 64) 128g of SO₂ is 128 / 64 = 2.0 moles

If 2.0 moles of SO₂ is produced, \({3 \over 4}\) × 2.0 = 1.5 moles of CaSO₄ will be required.

Thus 1.5 mol is the correct answer.

The formula of the metal bromide is MBr₃. This tells us that one mole of metal atoms will combine with three moles of bromine atoms (1:3).

Using Moles (mol) = mass (g) / molar mass (g mol⁻¹), 24 g of bromine is 24 / 80 = 0.3 moles (the common multiple for mental arithmetic here is 8)

Using the ratio 3:1, 0.3 moles of bromine combines with 0.1 moles of metal, M.

So if 0.1 moles of metal M has a mass of 18.1 g (given in the question) then 1 mole of metal M will have a mass of 18.1 × 10 = 181 g

Therefore the relative atomic mass of metal M is 181.

We need to find the simplest ratio of the number of (moles of) atoms. We cannot use a calculator so we will need to approximate the relative atomic masses that we take from the periodic table (e.g. carbon 12.01 = 12).

Start by assuming 100g: Thus 85.6g of C atoms, 14.4g of H atoms:

This suggests that the empirical formula is probably CH₂. The empirical formula mass is therefore approximately 14 units (12 + 1+ 1).

168g mol⁻¹ is the molar mass (rounded to a whole number) and 168 / 14 = 12

So there are 12 empirical formula units (of CH₂) in the molecular formula.

Therefore the molecular formula is C₁₂H₂₄.

(Once the approximate 1:2 ratio of C:H is known, the last part can also be done by trial and error: 12×12 = 144, 144+24 = 168)

Percentage yield = (experimental yield / theoretical yield) × 100%

Moles = mass / molar mass

Moles of ethene = 14 / 28

Moles of ethanol = 12 / 46

The reaction has a 1:1 molar ratio as seen in the equation. So the theoretical yield of ethanol in moles will be the same as the moles of ethene.

Therefore the percentage yield will be: (moles of ethanol / moles of ethene) × 100%

= (12 / 46) / (14 / 28) × 100%

(The easiest way to deal with this is probably to remember that dividing by a fraction is the same as multiplying by the inverted (upside down) fraction. So...)

= \({12\over 46}\) × \({28\over 14}\) × 100%

= \({12\times28\times100 \over 14\times46}\)

The value for the water of crystallisation, x, can be found by finding the integer ratio of moles of MnCl₂ : moles of H₂O. (x is always given as a whole number.)

Moles (mol) = mass (g) / molar mass (g mol⁻¹)

The moles of MnCl₂ can be found using the mass of the anhydrous salt: 31.5 / 126 = \({1\over 4}\) = 0.25 mol

The mass of water can be found by subtracting the mass of anhydrous salt from hydrated salt: 36.0 − 31.5 = 4.5 g

And moles of water = 4.5 / 18 = \({1\over 4}\) = 0.25 mol

The ratio of moles of MnCl₂ : moles of H₂O is therefore 0.25 : 0.25 and the integer ratio is therefore 1 : 1.

The value of x is therefore 1.