Chapter 11: Reactant, Gases and Solutions

# 11.1-Limiting Reactants

## Reactions stop when one reactant is used up

When some magnesium carbonate is placed into a beaker of hydrochloric acid, you can tell a

**reaction**is taking place because you see lots of bubbles of gas being given offAfter a while, the amount of fizzing slows down

The reaction stops when all reactants is used up

Reactants that’s used up in called limiting

**reactants**Amount of product formed is directly proportional to amount of limiting reactant

Because if you add more reactant there will be more reactant particles, meaning more product

**particles**

## The amount of product depends on the limiting reactant

You can calculate mass of product formed in a reaction by using the mass of the limiting reactant and the balanced

**reaction**equationWrite out the balanced equation

Work out

**relative**formula massesFind out how many moles there are of the substance you know the mass of

Use balanced equation to work out how many moles there’ll be of the other substance

Use the number of moles to calculate the mass

# 11.2-Gases and Solutions

## One mole of any gas occupies 24dm3 at 20c

At the same temperature and pressure, equal number of moles of any gas will occupy the same volume

At room temperature and pressure one mole of any gas will occupy 24dm3

You can use this formula to find the volume of a known mass of any gas

Volume of gas = mass of gas / Mr of gas x 24

## You can calculate volumes of gases in reactions

For reactions between gases,you can use the volume of one gas to find the volume of another

## Concentration is a measure of how crowded things are

Lots of reactions in chemistry take place between substances that are

**dissolved**in a a solutionThe amount of a substance in a certain volume of a solution is called its concentration

The more

**solute**there is in a given volume, the more concentrated the solutionOne way to measure the concentration of a

**solution**is by calculating the mass of a substance in a given volume of solutionThe units will be units of mass/units of volume

Concentration = mass of solute / volume of solvent

Concentration = number of moles of solute / volume of solvent

# 11.3-Concentration Calculations

## You might be asked to calculate the concentration

**Titrations**are experiments that let you find the volumes needed for two solutions to react together completelyIf you know the concentration of one of the solutions, you can use the volumes from the

**titration**experiment, along with the reaction equation, to find the concentration of the other solution

## Find the concentration in mol/dm3

You might remember the formula for working out the concentration of a substance in mol/dm3, this time it’s used in a triangle

No of moles

Concentration x volume

Work out how many moles of the known substance you have using equation

Work out concentration of unknown stuff

## Converting mol/dm3 to g/dm3

To find the concentration in g/dm3 start by finding the concentration in mol/dm3 using the steps above

Then convert the concentration in mol/dm3 to g/dm3 using the equation mass=moles x M

Work out the

**relative**formula mass for the acidConvert the concentration in moles into concentration in grams

## Practice Questions:

25.00cm^3 of 0.100mol/dm^3 neutralised by 20.00cm^3 of another solution

Do 25cm/1000 = 0.0250

Equation: concentration in mol/dm^3 = amount of solute in mol / volume in dm

0.100 x 0.0250 = 0.0025Mole ratio is1:1

20 / 1000 = 0.02

0.0025 / 0.02 =.125

In a titration, 25.00 cm3 of 0.200 mol/dm3 sodium hydroxide solution is exactly neutralised by 22.70 cm3 of a dilute solution of hydrochloric acid.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Calculate the concentration of the hydrochloric acid.

Volume of sodium hydroxide solution = 25.00 ÷ 1000 = 0.0250 dm3

Amount of sodium hydroxide = 0.200 × 0.0250 = 0.005 mol

From the equation, 0.005 mol of NaOH reacts with 0.005 mol of HCl

Volume of hydrochloric acid = 22.70 ÷ 1000 = 0.0227 dm3

Concentration of hydrochloric acid = 0.005 mol ÷ 0.0227

= 0.220 mol/dm3

# Chapter 11: Reactant, Gases and Solutions

# 11.1-Limiting Reactants

## Reactions stop when one reactant is used up

When some magnesium carbonate is placed into a beaker of hydrochloric acid, you can tell a

**reaction**is taking place because you see lots of bubbles of gas being given offAfter a while, the amount of fizzing slows down

The reaction stops when all reactants is used up

Reactants that’s used up in called limiting

**reactants**Amount of product formed is directly proportional to amount of limiting reactant

Because if you add more reactant there will be more reactant particles, meaning more product

**particles**

## The amount of product depends on the limiting reactant

You can calculate mass of product formed in a reaction by using the mass of the limiting reactant and the balanced

**reaction**equationWrite out the balanced equation

Work out

**relative**formula massesFind out how many moles there are of the substance you know the mass of

Use balanced equation to work out how many moles there’ll be of the other substance

Use the number of moles to calculate the mass

# 11.2-Gases and Solutions

## One mole of any gas occupies 24dm3 at 20c

At the same temperature and pressure, equal number of moles of any gas will occupy the same volume

At room temperature and pressure one mole of any gas will occupy 24dm3

You can use this formula to find the volume of a known mass of any gas

Volume of gas = mass of gas / Mr of gas x 24

## You can calculate volumes of gases in reactions

For reactions between gases,you can use the volume of one gas to find the volume of another

## Concentration is a measure of how crowded things are

Lots of reactions in chemistry take place between substances that are

**dissolved**in a a solutionThe amount of a substance in a certain volume of a solution is called its concentration

The more

**solute**there is in a given volume, the more concentrated the solutionOne way to measure the concentration of a

**solution**is by calculating the mass of a substance in a given volume of solutionThe units will be units of mass/units of volume

Concentration = mass of solute / volume of solvent

Concentration = number of moles of solute / volume of solvent

# 11.3-Concentration Calculations

## You might be asked to calculate the concentration

**Titrations**are experiments that let you find the volumes needed for two solutions to react together completelyIf you know the concentration of one of the solutions, you can use the volumes from the

**titration**experiment, along with the reaction equation, to find the concentration of the other solution

## Find the concentration in mol/dm3

You might remember the formula for working out the concentration of a substance in mol/dm3, this time it’s used in a triangle

No of moles

Concentration x volume

Work out how many moles of the known substance you have using equation

Work out concentration of unknown stuff

## Converting mol/dm3 to g/dm3

To find the concentration in g/dm3 start by finding the concentration in mol/dm3 using the steps above

Then convert the concentration in mol/dm3 to g/dm3 using the equation mass=moles x M

Work out the

**relative**formula mass for the acidConvert the concentration in moles into concentration in grams

## Practice Questions:

25.00cm^3 of 0.100mol/dm^3 neutralised by 20.00cm^3 of another solution

Do 25cm/1000 = 0.0250

Equation: concentration in mol/dm^3 = amount of solute in mol / volume in dm

0.100 x 0.0250 = 0.0025Mole ratio is1:1

20 / 1000 = 0.02

0.0025 / 0.02 =.125

In a titration, 25.00 cm3 of 0.200 mol/dm3 sodium hydroxide solution is exactly neutralised by 22.70 cm3 of a dilute solution of hydrochloric acid.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

Calculate the concentration of the hydrochloric acid.

Volume of sodium hydroxide solution = 25.00 ÷ 1000 = 0.0250 dm3

Amount of sodium hydroxide = 0.200 × 0.0250 = 0.005 mol

From the equation, 0.005 mol of NaOH reacts with 0.005 mol of HCl

Volume of hydrochloric acid = 22.70 ÷ 1000 = 0.0227 dm3

Concentration of hydrochloric acid = 0.005 mol ÷ 0.0227

= 0.220 mol/dm3