Making standard solutions

Question 1

one substance needed in a titration is

Answer 1

a standard solution

Question 2

a standard solution is

Answer 2

a solution whose concentration is accurately known

Question 3

one obvious way to prepare standard solution sis to

Answer 3

take a known mass of a substance and dissolve it in a known volume of water

Question 4

primary standards are

Answer 4

substances used to make a standard solution by weighing

Question 5

ideally, primary standards should be (6 items);

Answer 5

be solids with high molar masses
be available in a high degree of purity
be chemically stable (does not decompose or react with substances in the air)
not absorb water from the atmosphere
be soluble in water
react rapidly and completely with other substances when used in titrations

Question 6

unfortunately, several substances that are often used in titrations are not suitable as

Answer 6

primary standards

Question 7

hydrochloric is not a suitable primary standard because

Answer 7

it does not exist as a solid

Question 8

sodium hydroxide is not a suitable primary standard because

Answer 8

it absorbs water vapour and carbon dioxide from the atmosphere

Question 9

sodium carbonate is

Answer 9

white in colour and often seen on the necks of bottles of sodium hydroxide

Question 10

sulfamic acid is a

Answer 10

readily available primary standard to use in acid-base titrations

Question 11

sulfamic acid has formula

Answer 11

NH2SO3H

Question 12

before weighing your primary standard you need to

Answer 12

have a rough idea of the approximate concentration and volume of the solution to be made

Question 13

typical values for concentration and volume of primary solutions are

Answer 13

0.1 mol dm-3 and 250 cm3

Question 14

sulfamic acid has molar mass

Answer 14

97.1 g mol-1

Question 15

n= in terms of concentration

Answer 15

n= c x V

Question 16

to prepare a standard solution of sulfamic acid, we use the method; (8 items)

Answer 16

1) add between 2.3g and 2.5g of sulfamic acid to the weighing boat and weigh accurately
2) transfer as much as possible of the acid to a clean beaker and reweigh the weighing boat
3) add about 100 cm3 of deionised water to the beaker and stir until all of the sulfamic acid has dissolved
4) remove the stirring rod, using the deionised water to wash the rod into the beaker
5) place a funnel in the neck of the volumetric flask and pour the solution from the beaker into the flask
6) rinse the inside of the beaker several times with deionised water and transfer the washings to the flask
7) add deionised water to the flask and make up to the graduation mark
8) put the stopper in the flask and invert it several times to make a uniform solution

Question 17

when making a standard solution in a volumetric flask, it is important to ensure that the lowest part of the liquid (the meniscus) is

Answer 17

aligned with the graduation mark

Question 18

the lowest part of the liquid is called the

Answer 18

meniscus