2.1.4 Acids

Question 1

What is an acid

Answer 1

• proton donors
• when dissolved in water, the acid release H+ ion in to the solution
  Eg HCl + H2O —> H+ + Cl-

Question 2

What is a strong acid and give an example

Answer 2

acid release H+ ions and !completely dissociates!
Eg hydrochloric acid HCl
HCl —> H+ + Cl-

Question 3

What is a weak acid and give an example

Answer 3

acid release hydrogen ions into the solution and !partially dissociates!
Eg ethanoic acid CH3COOH
CH3COOH <=> H+ + CH3COO-
(Equilibrium indicates incomplete reaction)

Question 4

What are examples of bases

Answer 4

• metal oxide
• metal hydroxide
• metal carbonate
• ammonia

Question 5

What is a base and What does a base do

Answer 5

It is a proton accepter,
It neutralises an acid to form a salt

Question 6

What is an alkali and give an example

Answer 6

Usually Metal hydroxide
It’s a base that dissolves in water releasing hydroxide ions (OH-) into the solution
Eg NaOH + H2O —> Na+ + OH-

Question 7

What can titration be used for?

Answer 7

• Finding the concentration of a solution
• Identification of unknown chemicals
• Finding the purity of a substance

Question 8

How much is the volumetric flask filled?

Answer 8

The bottom of the meniscus of the liquid should be touching the graduation line

Question 9

What is the uncertainty of the burette? And how to calculate % uncertainty of a titre

Answer 9

Titre. x 100

Question 10

Equation and name of salt for MgO + HCl

Answer 10

MgO + 2HCl —> MgCl2 + H2O
Magnesium chloride

Question 11

What is an acid salt?

Answer 11

When one hydrogen atom has been replaced by a metal ion, but the other hydrogen atom can still behave as an acid

Question 12

How To carry out a titration

Answer 12

• Using a pippet measure 25cm³ of the standard solution and add it to a conical flask with a suitable indicator
• Add other solution into a burette till zero
• slowly open the tap while swirling the flask until the colour change slows down
• add drop by drop until endpoint is reached
• repeat until concordant results (0.1cm3)

Question 13

what is and How to prepare a standard solution

Answer 13

• it is A solution of known concentration
• Weigh the solid accurately using a two or more decimal place balance
• dissolve in distilled water in a beaker
• pour into a volumetric flask rinsing the beaker with more distilled water making sure to fill till exactly the graduation line (250cm3) view bottom of the meniscus at eye-level. Use a pipette when you’re close.
• invert flask several times for consistency

Question 14

What happens in a neutralisation reaction?

Answer 14

The acid react with a base to form a salt and water
Hydrogen in the acid is replaced by a metal or ammonium ion to form a salt
CuO + H2SO4 —> CuSO4 + H2O
exception - NH3(aq) + HCl(aq) → NH4Cl(aq)
no water is produced

Question 15

Hydrochloric acid and sodium hydroxide react, what is the salt?

Answer 15

Sodium chloride

Question 16

Sulphuric acid and copper oxide react what is is the salt formed

Answer 16

Copper sulphate

Question 17

Nitric acid and calcium carbonate react, what is the salt?

Answer 17

Calcium nitrate

Question 18

Ethanolic acid and ammonia react what is the salt?

Answer 18

Ammonium ethanoate

Question 19

Equation and name of salt for NaOH + H2SO4

Answer 19

2NaOH + H2SO4 —> Na2SO4 + 2H2O

Question 20

Equation and name of salt for ZnCO3 + HNO3

Answer 20

ZnCO3 + 2HNO3 —> Zn(NO3)2 + H2O + CO2
Zinc nitrate

Question 21

Equation and name of salt for NaOH + CH3COOH

Answer 21

CH3COONa + H2O

Question 22

Write equations for partial and complete neutralisation of carbonic acid with sodium hydroxide

Answer 22

H2CO3 + NaOH —> NaHCO3 + H2O
H2CO3 + 2NaOH —> NaCO3 + 2H2O

Question 23

Acid + metal carbonate =

Answer 23

Salt + H2O + CO2

Question 24

Full equation: HCl + NaOH —> NaCl + H2O
What is the ionic equation? What is the spectator ion?

Answer 24

H+ + OH- —> H2O
CL is a spectator ion

Question 25

Acid and metal

Answer 25

Salt and hydrogen

Question 26

What are the main acids?

Answer 26

HCl hydrochloric acid H2SO4 sulphuric acid HNO3 nitric acid CH3COOH ethanoic acid H3PO4 phosphoric acid

Question 27

What are the common alkalis?

Answer 27

NaOH sodium hydroxide KOH potassium hydroxide NH3 ammonia

Question 28

What does the dot formula indicate?

Answer 28

The amount of water present in a crystalline structure

Question 29

what is the systematic name of?SnCl2

Answer 29

Cl-1 x 2 = -2 Sn = +2 so II Tin(II) chloride

Question 30

How to work out percentage uncertainty given the initial and final readings

Answer 30

1. Work out the difference (=the titre) 2. Divide the uncertainty by the titre 3. X by 2 as there’s 2 values which go wrong 4. X by 100 for a percentage

Question 31

What do the the Roman numerals in the name of a compound represent

Answer 31

The charge of the ion they are next to

Question 32

write The reaction of ammonium carbonate with dilute nitric acid

Answer 32

(NH4)2CO3 + 2HNO3 → 2NH4NO3 + CO2 + H2O

Question 33

20.25 20.35 20.60 Calculate the mean titre

Answer 33

20.25+20.35/2 = 20.30 cm3

Question 34

Writing equation and oxidisation numbers of CH3COOH with magnesium, What has been oxidised and what has been reduced Include the Ionic equation

Answer 34

Mg + 2CH3COOH → (CH3COO)2Mg + H2 Mg + 2H+ → Mg2+ + H2 Oxidation:    Mg from 0 to +2 Reduction:    H from +1 to 0

Question 35

Explain why two different reactions with magnesium one with HCL and one with CH3COOH produce the same volume as gas at different rates

Answer 35

HCL is a strong acid which completely dissociates It has a greater concentration of H So has more frequent collisions therefore faster rate of reaction compared to ethanolic acid To produce the same moles of H in the end as ethanoic acid has a lower concentration and is a weak acid which partially dissociates

Question 36

Describe and explain the change in rate of mass of salts produced in a neutralisation reaction produced (curve going down)

Answer 36

Rate is decreasing as reactants are being used up and concentration decreases therefore less frequent collision occur

Question 37

How can we investigate mass of salt produced in a neutralisation reaction ?mention apparatus

Answer 37

Use a beaker, a balance and a stopwatch record the mass every 30 seconds and plot it in a results table

Question 38

How is a salt formed in a neutralisation reaction?

Answer 38

A hydrogen ION from the acid has been replaced by a metal ION

Question 39

How can we improve the titres accuracy

Answer 39

Repeat titration into two concordant results within 0.1cm3 are found and calculate a mean using only concordant results