4- Acids and Redox

Question 1

What are the common acids?

Answer 1

Hydrochloric acid - HCl
Sulfuric acid - H2SO4
Nitric Acid - HNO3
Ethanoic Acid - CH3COOH

Question 2

What are acids? What happens when they are dissolved in water?

Answer 2

-Proton donors
-They release hydrogen ions (H+) as protons when dissolved in water

Question 3

What is the equation for acids dissolving in water? Give the example of HCl

Answer 3

HA + H20 ⇌ H+ + A-

HCl + H20 → H+ + Cl-

Question 4

What is an example of a strong acid? How does it react with water?

Answer 4

-HCl, H2SO4, HNO3
-Strong acids release all there hydrogen atoms into a solution as H+ ions (forward reaction favoured sp lots of H+ formed)
-completely dissociates in aqueous solution

HCl → H+ + Cl -

Question 5

What is an example of a weak acid? How does it react with water?

Answer 5

-Ethanoic acid (CH3COOH)
-Only releases a small proportion of its available hydrogen atoms into solution as H+ ions (backward reaction is favoured so not as may H+ protons produced)
-only partially dissociates in aqueous solution

CH3COOH (aq) ⇌ H+ (aq) + CH3COO- (aq)

Question 6

What is an alkali? What is the overall equation and example of reaction with NaOH?

Answer 6

A base that dissolves in water releasing OH- ions into the solution

B + H20 ⇌ BH+ + OH-

NaOH + H20 ⇌ Na+ + OH-

Question 7

What does a base do?

Answer 7

-neutralises an acid to form a salt

Question 8

What happens when an alkali (base) dissolves in water?

Answer 8

-releases hydroxide (OH-) ions into the solution
-NaOH + H20 → Na+ + OH-

Question 9

What are some examples of common bases?

Answer 9

-Sodium hydroxide NaOH
-Potassium hydroxide KOH
-Ammonia NH3

Question 10

What is an example of a strong base? What happens when they react with water?

Answer 10

-NaOH , KOH
-forward reaction is favoured is favoured, lots of OH- ions formed

NaOH ⇌ Na+ + OH-

Question 11

What is an example of a weak base? What happens when they react with water?

Answer 11

-Ammonia NH3
-backward reaction is favoured, not as may OH- ions formed, only partially dissociates

NH3 + H20 ⇌ NH4+ + OH-

Question 12

What is a polyprotic acid? And examples

Answer 12

-An acid which donated more then one proton (H+)
-H2SO4 is diprotic (1 mol of H2SO4 donates 2 moles of H+)
-H3PO4 is triprotic (1 mol of H3PO4 donates 3 moles of H+)

Question 13

What are examples of common metal oxides?

Answer 13

-MgO
-CaO
-CuO

Question 14

What are examples of common metal carbonates?

Answer 14

-Na2CO3
-CaCO3
-CuCO3

Question 15

What happens when an acid and base reacts in a neutralisation reaction?

Answer 15

acid + base → salt + water
-H+ ions react with the OH- ions produced from the base (alkali) to form a salt and neutral water
-H+ ions from the acid are replaced by the metal or ammonium ions from the base
-salt is made from the metal from the base and the non metal from the acid

H+ + OH- → H20
HCl + LiOH → LiCl + H20
HNO3 + KOH → KNO3 + H20

Question 16

What happens when ammonia reacts with a base (alkali)?

Answer 16

-reacts with acids to make ammonium salts but no water

2NH3 + H2SO4 → (NH4)2SO4

Question 17

How does ammonia react with water?

Answer 17

-doesn’t produce OH- ions directly
-ammonia reacts with H2O first and accepts a proton to produce an ammonium ion (NH4+) and OH- ions

NH3 + H20 ⇌ NH4+ + OH-

Question 18

What is the fill equation and ionic equation of HCl (acid) reacting with NaOH (alkali) ?

Answer 18

full equation -
HCl + NaOH → NaCl + H20
H+ + OH- → H20

Question 19

What is the general reaction of a metal reacting with an acid?

Answer 19

Metal + Acid → Salt + Hydrogen

Question 20

What is the equation and ionic equation for Calcium (metal) reacting with H2SO4 (acid)?

Answer 20

Ca + H2SO4 → CaSO4 + H2
Ca + 2H+ → Ca2+ + H2

Question 21

What is the general reaction of a metal oxide reacting with an acid?

Answer 21

Metal oxide + acid → salt + water

Question 22

What is the equation and ionic equation for magnesium oxide reacting with HCl (acid)?

Answer 22

MgO + 2HCl → MgCl2 + H20
MgO + 2H+ → Mg 2+ + H2O

Question 23

What is the general reaction of a metal hydroxide reacting with an acid?

Answer 23

metal hydroxide + acid → salt + water

Question 24

What is the equation and ionic equation for sodium hydroxide reacting with sulfuric acid?

Answer 24

2NaOH (aq) + H2SO4 (aq)→ NaSO4 + 2H2O
2 OH- (aq) + 2H+ (aq) → 2H2O

Question 25

What is the general equation for the reaction of an acid with a metal carbonate?

Answer 25

Metal carbonate + Acid → Salt + Carbon dioxide + Water

Question 26

What is the equation and ionic equation for lithium carbonate reacting with nitric acid (acid)?

Answer 26

LiCO3 (s) + 2HNO3 (aq) → 2LiNO (aq) + CO2 (g) + H2O (g)
LiCO3 (s) + 2H+ (aq) → 2Li+ (aq) + CO2 (g) + H2O (g)

Question 27

What do H+ ions and OH- ions form when reacting together?

Answer 27

Neutral water

Question 28

What can titrations be used for?

Answer 28

-finding the concentration of a solution
-identification of unknown solutions
-finding the purity of a substance

Question 29

What is a standard solution?

Answer 29

A solution of known concentration

Question 30

What is the typical tolerance of a 100cm3 volumetric flask?

Answer 30

±0.20 cm^3

Question 31

What is the typical tolerance of a 250cm3 volumetric flask?

Answer 31

±0.30 cm^3

Question 32

What is the method for preparing a standard solution?

Answer 32

1. Weigh out the solid precisely using a balance and a weighing boat
2. Transfer the solid from the weighing boat to a beaker.
3. Dissolve your solid fully using less distilled water than will be needed to fill the volumetric flask to the mark. Stir to ensure the solid is dissolved fully with a glass rod
4. Transfer your solid to a volumetric flask. Use a funnel to avoid spillage. Rinse the beaker and glass rode into the flask with distilled water to make sure all of the solution is transferred
5. Using distilled water fill the volumetric drop by drop until the bottom of meniscus lines up directly with the graduation line
6. Slowly, invert the flask a few times to ensure the solution is thoroughly mixed

Question 33

What is the uncertainty of a 10cm3 and a 20cm3 pipette and a 50cm3 burette?

Answer 33

10cm3 pipette - ±0.04 cm^3
20cm3 pipette - ±0.06 cm^3
50cm3 burette - ±0.10cm^3

Question 34

What is each burette reading measured to?

Answer 34

The nearest ±0.05cm3 , so it always had 2 decimal places

Question 35

How do you carry out an acid-base titration procedure?

Answer 35

1. Add a measured volume of one solution to a conical flask using a pipette
2. add the other solution to a burette, and record the initial burette, reading to the nearest 0.05 cm³
3. A few drops of indicator to the solution in the conical flask.
4. Run the solution in the burette into the solution in the conical flask, swirling the conical flask throughout.
5. keep going until the indicator changes colour at the end point of the titration
6. Record the final burette reading. the volume of solution added from the burette is called the titre, which is calculated by subtracting the initial from the final burette reading
7. A quick trial titration is carried out 1st to find the approximate titre
8. the titration is repeated accurately, adding the solution drop wise as the endpoint is approached, until two accurate tires are concordant (within 0.10 cm³)

Question 36

how do you work out the mean titre?

Answer 36

-Only use values which are concordant (within 0.10 cm³), you can reject inaccurate titres
-If you were to include all the titres in the mean, you would have lost the accuracy of the titration technique