Acids/Alkalis/Titrations/mole calculations and formulae

Question 1

State a substance with a pH of 4-6

Answer 1

Ethanoic acid (vinegar)

Question 2

State a substance with a pH of 8-10

Answer 2

Ammonia

Question 3

State a substance of a pH between 11-14

Answer 3

Sodium hydroxide

Question 4

State a substance with a pH of 7

Answer 4

Sodium chloride

Question 5

State the definition of an acid

Answer 5

An acid is a substance that acts as a source of excess hydrogen ions (H+) in a solution

Question 6

State the definition of an alkali

Answer 6

An alkali is a substance that acts as a source of excess hydroxide (OH-) ions in a solution

Question 7

State the definition of a base

Answer 7

A substance that neutralizes acids by absorbing hydrogen ions

Question 8

Is the reaction of CuO(s) + HCl(aq) —-) CuCl2(aq) a reaction of a base and an acid or an alkali and an acid

Answer 8

Base and an acid
(Does not contain OH ions and CuO is insoluble so not aqeous)

Question 9

Give three examples of three types of substances that can be a base

Answer 9

1)metal carbonate
2)metal hydroxide
3) metal oxide

Question 10

Write the equation for when sodium hydroxide ionizes (dissociates) with state symbols

Answer 10

NaOH(aq) —) Na+(aq) + OH-(aq)

Question 11

Write the equation for when sulfuric acid ionizes

Answer 11

H2SO4(aq) —-) 2H+(aq) + SO4 2-(aq)

Question 12

What colour does litmus turn in acid and then alkali solutions

Answer 12

Acid= red
Alkali= blue

Question 13

What colour does methyl organge turn in acid and then alkali solutions

Answer 13

Acid= Red
Alkali= Yellow

Question 14

What colour does phenolphthalein turn in acid and then alkali solutions

Answer 14

Acid= colourless
alkali= pink

Question 15

Name four method that can be used to measure pH

Answer 15

Litmus
Universal indicator
Methyl orange
Phenolphthalein

Question 16

What colour is methyl orange in neutral solutions

Answer 16

Yellow

Question 17

If the number of H+ ions in a solution decreases, does the pH increase or decrease

Answer 17

Increases

Question 18

What colour is litmus in neutral solutions

Answer 18

Purple

Question 19

What colour is phenolphthalein in neutral solutions

Answer 19

Colourless

Question 20

What is a neutralization reaction

Answer 20

A reaction between an acid and a base

Question 21

Write the ionic equation of the reaction between Sodium hydroxide and hydrochloric acid
(All neutralization reactions have same ionic equation btw)

Answer 21

OH-(aq) + H+(aq) —-) H2O

(Sodium and chloride ions are same on both side so not included in equation)

Question 22

Write the equation for the reaction of copper (ii) oxide and dilute sulfuric acid

Answer 22

CuO + H2SO4 —-) CuSO4 + H2O
(Copper oxide + sulfuric acid —-) copper sulphate + water)

Question 23

Definition of a strong acid

Answer 23

Acid in which ions have completely dissociated

Question 24

Definition of a weak acid

Answer 24

Acid in which ions have only partially dissociated

Question 25

What is a titre

Answer 25

The volume of acid or alkali being added
So the difference between the initial reading on the biuret and the final reading

Question 26

Explain how to carry out a neutralization titration using phenolphthalein, where trying to calculate how much sodium hydroxide is needed to neutralize hydrochloric acid

Answer 26

1)Use a pipette and pipette filler (for safety) to measure 25cm3 of hydrochloric acid and add to a conical flask
2)Add a few drops of phenolphthalein indicator to the conical flask
3)Fill the burette with sodium hydroxide and take initial reading to 2 decimal places
4) keep adding drops to flask and swirling it until solution turns pink
5measure final reading and repeat experiment until concordant results are obtained

Question 27

Explain Why it is better to use phenolphthalein rather than universal indicator in a titration (2)

Answer 27

Phenolphthalein has only two colours
But universal indicator has a range of colours
The colour change in phenolphthalein us sudden
But the colourless change in universal indicator is gradual
so the exact amount at which the neutralization occurs would be unknown in universal indicator

Question 28

When recording measurements on a burette how many decimal places should it be till?

Answer 28

2 decimal places
(Burette is the long dagger tube thing)

Question 29

Explain how you can carry out an experiment using reduction to test the empirical formula of copper oxide

Answer 29

1)measure the mass of a test tube that has a bung with a hole in it
2) place copper oxide inside and measure the mass again
3)turn hydrogen gas on and insert it through the hole in the bung and then begin to pass heat over the test tube
4)once black copper oxide has turned a brown-pink colour weigh the mass of the test tube again as a final reading
5)the initial mass of copper oxide will be (mass of test tube + copper oxide - mass of test tube)
6)the final mass of copper oxide will be (mass of test tube+ final mass of copper oxide - mass of test tube)
7)mass of final copper oxide - initial mass of copper oxide = mass of oxygen

Question 30

Why can you not find the molecular formula of NaCl

Answer 30

Because it is an ionic compound and is not made up of molecules

Question 31

H20 + HCL —-) H3O+ + CL-
So explain why the chlorine atom has a negative charge on the products side

Answer 31

Because the H+ ion left an electron behind when it transferred to the water molecule

Question 32

Definition of an acid, in terms of proton transfer

Answer 32

defined as a proton (or hydrogen ion) donor

Question 33

Definition of a base (in terms of proton transfer)

Answer 33

Defined as a proton (hydrogen ion) acceptor

Question 34

Write the ionic equation of the reaction between water and hydrochloric acid (in terms of proton transfer)

Answer 34

H2O(l) + HCL(aq) —-) H3O+(aq) + CL-(aq)

Question 35

Write the ionic equation of the reaction between ammonia and hydrochloric acid (in terms of proton transfer)

Answer 35

NH3(aq) + HCL(aq) —-) NH4+(aq) + CL-(aq)