QUESTION 1 [10 MARKS] a) An experiment is carried out the reaction between solid sodium carbonate with aqueous
hydrogen sulphate to form aqueous sodium sulphate, carbon dioxide and water.

Na2CO3
H2SO4 ->
Na SO4 +
CO2 + H2O

i) Rewrite the given equation by adding an appropriate state symbols.

[1 mark]
ii) Calculate the number of moles of hydrogen sulphate required to react with 2.12 g of sodium
carbonate.

[2 marks]

iii) Calculate the concentration of sodium carbonate solution which prepared from 2.12 g of
sodium carbonate in 250.0 cm of volumetric flask.

[2 marks]

a:

by the combination of an unlimited number of elements

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.

a electronegativity decreases beacuse the size of nucleus is bigger.