chemistry p1

Question 1

why might the percentage yield of a chemical reaction be less than 100%

Answer 1

-the reactants dont all react (e.g. because the reaction is slow or reaches equilibrium)
-there may be side reactions, meaning that other products are produced instead
-some of the products may be lost

Question 2

moles

Answer 2

mass/Mr

Question 3

percentage yield

Answer 3

actual yield/ theoretical yield x100

Question 4

atom economy

Answer 4

Mr of desired product/ Mr of all reactants x100

Question 5

cocentration

Answer 5

mass of solute/volume of solvent

number of moles of solute/ volume of solvent

Question 6

percentage mass of an element in a compound

Answer 6

(Ar x number of atoms in that element)/ (Mr of compound) x100

Question 7

volume of gas

Answer 7

mass/Mr x 24

or

moles x 24

Question 8

what describes the strength of an acid

Answer 8

the proportion of acid molecules which dissociate into hydrogen ions

Question 9

acid + metal oxide

Answer 9

salt + water

Question 10

what is a neutralisation reaction

Answer 10

acid + base

Question 11

acid + metal hydroxide

Answer 11

salt + water

Question 12

metal + acid

Answer 12

salt + hydrogen

redox reaction!

Question 13

metal + water

Answer 13

base (metal hydroxide) + hydrogen

Question 14

single indicators for titrations

Answer 14

litmud
(blue alkali, red acid)

methyl orange
(yellow alkali, red acid)

phenolphthalein
(pink alkali, colourless acid)

Question 15

why is a burette appropriate for acids in titrations

Answer 15

• measures variable volumes
• more accurate than a cylinder
• allows you to add it in drops near the end point

Question 16

why is a pipette appropriate for alkalis in titrations

Answer 16

• measures only a fixed volume of a solution