Measuring pH

Question 1

[x] means

Answer 1

the concentration of x

Question 2

what is the equation to show when water molecules undergo self ionisation

Answer 2

H2O(l) + H2O(l) ⇌ H3O+(aq) + OH−(aq)

Question 3

how does water behave when reacting with itself

Answer 3

as both a very weak base and very weak acid

Question 4

Kw

Answer 4

ionic product of water

Question 5

formula to calculate Kw

Answer 5

[H3O+][OH-]=1x10^-14 at 25°C

Question 6

how is the Kw formula justified

Answer 6

all aqeuous solutions conatin H3O+ ions and OH- ions and the product of their molar concentrations is always 1x10^-14 at 25°C and therfore if either [H3O+][OH-]increases than the concentration of the other must decrease proportionatley

Question 7

formula to calculate concentration of H3O+ from known concentration of OH-

Answer 7

[H3O+] = 1x10^-14/[OH-]

Question 8

formula to calculate concentration of OH- from known concentration of H3O+

Answer 8

[OH-} = 1x10^-14/[H3O+]

Question 9

[H3O+][OH-] is known as

Answer 9

the ionic product of water

Question 10

in pure water and neutral solutions [H3O+]

Answer 10

10^-7

Question 11

in pure water and neutral solutions [OH-]

Answer 11

10^-7

Question 12

in acidic solutions [H3O+]

Answer 12

[H3O+]>10^-7

Question 13

in acidic solutions [OH-]

Answer 13

[OH-}<10^-7

Question 14

in basic solutions [H3O+]

Answer 14

[H3O+]<10^-7

Question 15

in basic solutions [OH-]

Answer 15

[OH-}>10^-7

Question 16

how to calculate [H3O+] from known acid concentration

Answer 16

if the acid contains 1 hydrogen atom, its [H3O+] is equal to its concentration,if the acid contains 2 hydrogen atoms its [H3O+] is double its concentration

Question 17

how to calculate [OH-] from base

Answer 17

if the base contains 1 hydrogen atom, its [OH-] is equal to its concentration,if the base contains 2 hydrogen atoms its [OH-] is double its concentration

Question 18

formula to calculate pH

Answer 18

pH=-log10[H3O+]

Question 19

at 25°C, neutral solutions have a pH of

Answer 19

7

Question 20

at 25°C, acidic solutions have a pH of

Answer 20

less than 7

Question 21

at 25°C, basic solutions have a pH of

Answer 21

more than 7

Question 22

a solution of pH 2 has how many more H3O+ ions than a pH of 3

Answer 22

ten times the concentration of the H3O+

Question 23

how to calculate the [H3O+] from known pH

Answer 23

[H3O+] = 10^-pH

Question 24

pH metres do what

Answer 24

provide a specific quantitative measurement of pH

Question 25

how do pH metres work

Answer 25

by measuring the difference in electrical potential between two probes due to the concentration of charged particles or ions in the solution

Question 26

what are indicators

Answer 26

substances that change colour when they are added to an acidic or basic solution

Question 27

what is universal indicator

Answer 27

a mixture of a variety of other indicators that can be used to measure the approximate pH of a solution

Question 28

litmus paperr

Answer 28

one of tthe simplest and most common indicatorrs which uses a dye derived from lichens

Question 29

litmus paper in acidic solutions

Answer 29

blue litmus paper will turn red

Question 30

littmus paper in basic solutions

Answer 30

red litmus paper will turn blue

Question 31

why as indicators less accurate then pH metres

Answer 31

indicators only provide a pH range for a given solution

Question 32

accuracy of pH metres

Answer 32

highly accurate, usually correct to +-0.01 pH uints and is built into the calibration of the metre

Question 33

why are pH metres more precise

Answer 33

because there is no change to the calibration of the instrument between measurements

Question 34

why are indicators less precise

Answer 34

the estimated pH of a given solution may differ greatly between multiple trials

Question 35

end point

Answer 35

the point at which the indicator changes colour