Week 3

Question 1

1amu (atomic mass unit) =

Answer 1

1/12th the mass on an atom of Carbon-12 = 6.022 x 10^-23

Not convenient so we define the quantity which is equal to 12g of Carbon-12 to be 1 mole

Question 2

Define mole

Answer 2

1 mole, or the amount equal to the atomic mass in grams of any substance contains 6.022x10^23 atoms of that substance

Question 3

What is Avogadro’s constant?
(Na)

Answer 3

Na = 6.022 x 10^23 mol-1

Question 4

What is molecular mass (molar mass)

Answer 4

The mass of one mole of any compound = the sun of relative atomic masses of all the elements which make up the compound (g)

How much 1mole of a molecule/compound weighs in grams

Question 5

What is the equation to work out number of moles

Answer 5

Number of moles = Mass in grams / Molar mass

N = m / M

Question 6

What is Variance

Answer 6

The summation of the difference of each point from the mean squared, then averaged (divided by n)

Question 7

What is n in standard deviations ?

Answer 7

The number of observations in your data

Question 8

When is the statistical T-test used?

Answer 8

Small sample
Normal distribution
Two groups
Numeric data
One variable of interest

Question 9

When is the statistical z-test used?

Answer 9

Large sample
Normal distribution
Two groups (independent)
Numeric data
One variable of interest

Question 10

What is relative molecular mass?

Answer 10

How much 1 molecule/compound weighs relative to a C-12 atom

Question 11

What is the difference between the units amu and Da?

Answer 11

amu (Atomic mass units) and Da (Daltons) means the same thing: the mass of one molecule (glucose for example) is 180 times the mass of a carbon-12 atom

Biologists like to use Da as its simpler than amu

Question 12

If the Mr of cytochrome c is 12,000. How many moles of cytochrome c are present in 1ml of a 5μg/ml solution of cytochrome c​

Answer 12

12,000 = Molar mass (m)
5ug/mL = M
So, for every 1ml solution there are 5ug/mL of cytochrome C

1ug = 10^-6g
So, there are 5 x 10^-6g in 1mL

Moles = 5 x 10^-6 / 12,000g
Moles = 4.17 x 10^-10mols

Moles = Mass (g) / Molecular Mass (g/mol)

Question 13

Unit for relative molecular mass (in an equation)

Answer 13

Mr

Question 14

Calculate the number of moles present in 5 mg citric acid. ​

Answer 14

5 mg = 5 x 10-3 g = 0.005 g​

Molar mass (M) of citric acid = 192.12 g​

Therefore, the number of moles present in 5 mg = 5 x 10-3/ 192.12​

							= 2.6 x 10-5​

							= 26 x 10-6​

							= 26 umoles​

Question 15

Molarity of a solution measures….

Answer 15

The number of moles of a substance in a certain volume

Units: mol/l or mol l^-1 or M

Question 16

Molarity units versus molar mass units?

Answer 16

M = Moles per liter

Molar mass = grams per mole

Question 17

Formulae for molarity?

Answer 17

M = no of moles of solute / volume of solution (L)

Question 18

Example question: Give the number of moles, molecules and grams in 12.1nmol of NADH

Answer 18

Moles = 12.1 x 10^-9mols

Molecules = 7.29x10^15

Mass = 8.02 x 10^-6g/mol

Mass = moles x mw
Molecules = moles x avogadros constant (6.022x10^23)

Question 19

How many molecules are there in 1L of a 3g/L solution of Lactose (mw=342.3g/mol)​

Answer 19

First convert grams into moles: n=m/M
n = 3/342.3g/mol
n= 0.00876moles

Then convert moles to molecules:
Molecules = 0.00876 x (6.022x10^23)
Molecules = 5.27 x 10^21

Question 20

The molecular weight of haemoglobin is about 65,000 g/mol. Haemoglobin contains 0.35% Fe by mass. How many iron atoms are there in a haemoglobin molecule?

Answer 20

MW = 65,000
Atomic mass number of Fe = 56
Mass of Fe in Hb = 0.35%
So, 0.35x65000 / 100
= 227.5
Therefore, number of Fe atoms in a Hb molecule = 227.5 / 56
= 4.06

Question 21

Formula for calculating molar concentration?

Answer 21

Molar concentration (c) = number of moles (n) per letre volume (v)

c = n / v so…. n = cv

This can be used for making solutions!