Elements of Life

Question 1

A student carries out a titration. NaOH solution is transferred to a conical flask using a pipette. Methyl orange indicator is added to the flask. HCl is added from a burette until the indicator changes colour. What would lead to the titre being larger than it should be?

Answer 1

Rinsing the burette with water before filling it with hydrochloric acid.

Question 2

Which of the below does the absorption spectrum of atomic hydrogen provide evidence for?

1: the excitation of electrons
2: the existence of discrete energy levels
3: the strength of the hydrogen–hydrogen bond

Answer 2

1: the excitation of electrons
2: the existence of discrete energy levels

Question 3

A 0.20 g sample of an acid HX requires 8.0 cm3 of 0.40 mol dm–3 sodium hydroxide for complete reaction. What is the relative molecular mass of the acid?

Answer 3

HX + NaOH –> NaX + H2O

There’s 0.0032 moles of NaOH, and 0.0032 moles of HX. Mr=mass/moles. Therefore Mr=62.5

Question 4

Describe the procedure for carrying out a flame test and give the colour of the flame that calcium produces.

Answer 4

Nichrome wire dipped in sample and concentrated HCl
then placed in blue/roaring Bunsen flame
(Brick) red

Question 5

What method is used to determine the mass and the relative abundance of isotopes in a sample?

Answer 5

Mass spectrometry