Mrs Chana qs

Question 1

Recall the formula of the following substances: • hydrochloric acid and ethanoic acid • carbon dioxide, hydrogen and water • sodium chloride and potassium chloride • ammonia and calcium carbonate.

Answer 1

HCl CH3OOH
CO2 H2 H2O
NaCl KCl
NH3 CaCO3

Question 2

Recall the formula of the following substances: • sulfuric acid and nitric acid • sodium hydroxide, potassium hydroxide and magnesium carbonate • sodium sulfate, potassium sulfate, magnesium sulfate and barium sulfate • lead(II) nitrate and lead iodide • potassium iodide and potassium nitrate

Answer 2

H2SO4 H2NO3
KOH MgCO3
NaSO4 KSO4 MgSO4 BaSO4
Pb(NO3)2 
PbI2 KI2 KNO3

Question 3

Recall and use the relationship between molar mass, number of moles and mass:

Answer 3

number of moles = mass ÷ molar mass • determine the number of moles of an element from the mass of that element • determine the number of moles of a compound from the mass of that compound • determine the masses of the different elements present in a given number of moles of a compound.

Question 4

What is relative atomic mass

Answer 4

the average mass of an atom of the element compared to the mass of 1/12th of an atom of carbon-12.

Question 5

Recall and use the relationship between molar mass, number of moles and mass:

Answer 5

• number of moles = mass ÷ molar mass. Determine the number of moles of an element from the mass of that element.

Question 6

Recall and use the relationship between the amount in moles, concentration in mol/dm3 and volume in dm3:

Answer 6

• amount in moles = concentration × volume • concentration = amount in moles ÷ volume • volume = amount in moles ÷ concentration.

Question 7

Explain the need for several consistent titre readings in titrations.

Answer 7

The titre is used to work out the concentration of either the acid or the alkali, provided the concentration of the other one is known. It is important that the titre is accurate, otherwise the calculated concentration will be wrong.
A titration is repeated until several consistent titres are obtained. Any anomalous titres (ones that are too high or too low compared to the others) are ignored, and the mean titre is calculated.

Question 8

Recall and use the relationship between the amount in moles, concentration in mol/dm3 and volume in dm3:

Answer 8

• amount in moles = concentration × volume • concentration = amount in moles ÷ volume • volume = amount in moles ÷ concentration.

Question 9

Describe the difference in colour change during a titration using a single indicator, such as litmus or phenolphthalein, compared to a mixed indicator, such as universal.

Answer 9

Single indicators contain a single substance which changes colour at the end point.
Mixed indicators contain many different indicators which change colour over a series of pHs

Question 10

Explain why an acid-base titration should use a single indicator rather than a mixed indicator.

Answer 10

Because there is a sudden colour change at the end point

Question 11

Describe an experimental method to measure the volume of gas produced in a reaction given appropriate details about the reaction.

Answer 11

Gas syringe or upturned measuring cylinder or weighing before and after

Question 12

Formula for moles of gas

Answer 12

amount = volume of gas ÷ molar volume of gas at rtp at rtp (24)

Question 13

How gas volumes change during the course of a reaction

Answer 13

Increase and then level off because of the limiting reactant

Question 14

Recall that in a reversible reaction at equilibrium:

Answer 14

• the rate of the forward reaction equals the rate of the backward reaction • the concentrations of the reactants and the products do not change.
It is on the left if the concentration of reactants is greater
than the concentration of products.
• It is on the right if the concentration of products is
greater than the concentration of reactants.

Question 15

Explain why a reversible reaction may reach an equilibrium: •

Answer 15

importance of a closed system • initially rate of forward reaction decreases • initially rate of backward reaction increases • eventually rate of forward equals rate of backward reaction.

Question 16

Factors that affect the position of equilibrium

Answer 16

removing a product moves the position of equilibrium to the right or vice versa • adding extra reactant moves the position of equilibrium to the right or vice versa • increasing the temperature moves the position of equilibrium in the direction of the endothermic reaction or vice versa • increasing the pressure moves the position of equilibrium to the side with the least number of moles of gas molecules or vice versa. Explain the effect of changing product concentration, reactant concentration, temperature or pressure on the position of equilibrium given appropriate details about a reaction.

Question 17

The contact process reactions and stages

Answer 17

There are three stages
S + O2 → SO2
2SO2 +O2->< 2SO3
SO3 + H2O → H2SO4

Stage two- the reaction between sulfur dioxide and oxygen is reversible

Understand that the reaction between sulfur dioxide and oxygen is reversible: • sulfur dioxide + oxygen sulfur trioxide • 2SO2(g) + O2(g) 2SO3(g) Describe the conditions used in the Contact Process: • V2O5 catalyst • around 450°C • atmospheric pressure.

Question 18

Explain the conditions of the contact process:
-V2O5 catalyst
-450C
Atmospheric pressure

Answer 18

Explain the conditions used in the Contact Process: • increasing the temperature moves the position of equilibrium to the left and increases rate of reaction so a compromise temperature is used • addition of catalyst increases rate but does not change position of equilibrium • even at low pressure, the position of equilibrium is already on right so expensive high pressure is not needed.

Question 19

What do acids do when added to water

Difference between strong and weak acids

Answer 19

an acid ionises in water to produce H+ ions. Understand that a strong acid completely ionises in water and a weak acid does not fully ionise and forms an equilibrium mixture.

Question 20

What is the difference between acid strength and concentration

Answer 20

RQ why the pH of a weak acid is much higher • acid strength (strong or weak) is a measure of the degree of ionisation of the acid • acid concentration is a measure of the number of moles of acid in one dm3

Question 21

Why does ethanoic acid react slower than hydrochloric acid of the same concentration

Answer 21

• lower concentration of hydrogen ions to carry the charge in ethanoic acid.

Question 22

Why are most precipitation reactions fast

Answer 22

The collision frequency between ions in solution is very large. There is a high chance that different ions will collide with each other and cause a reaction, so precipitation reactions are extremely fast. Precipitates form as soon as two suitable solutions are mixed together

Question 23

Word equation for the reaction between barium chloride and sodium sulfate

Answer 23

Barium chloride+sodium sulfate-> barium sulfate +sodium chloride

Question 24

What are spectator ions

Answer 24

Ions that do not take part in the reaction

Question 25

How do you prepare a dry sample of an insoluble substance

Answer 25

mix solutions of reactants • filtration • wash and dry residue