11852 14 The recommended daily allowance for salt, sodium chloride, is 6.0 g. Eating too much salt can lead to high blood pressure, potentially causing heart disease and strokes. (a) State the electronic configuration of a sodium atom and use it to explain why sodium is regarded as an s-block element. [2] (b) (i) Define the term Avogadro’s constant. [1] (ii) Calculate the number of sodium ions in the recommended daily allowance of sodium chloride. [2] (c) A solid sample of salt was analysed to confirm the identity of the ions present. A flame test was first conducted on the sample using nichrome wire and concentrated hydrochloric acid to identify sodium ions. The presence of chloride ions was subsequently confirmed. (i) State two reasons why nichrome wire was used. [2] 11852 [Turn over (ii) State two reasons why concentrated hydrochloric acid was used. [2] (iii) State the colour observed in the flame test. [1] (d) Describe how the presence of chloride ions could be confirmed in the solid salt. [4] (e) A second salt sample was thought to be contaminated with sodium carbonate. Describe a chemical test to confirm the presence of carbonate ions. [3] 11852 (f) The salt sample, of mass 6.0 g, contaminated with sodium carbonate was dissolved in water. A solution of magnesium chloride was added, forming a precipitate of magnesium carbonate. The precipitate was filtered off and dried to give 1.4 g of magnesium carbonate. (i) Draw a dot and cross diagram to show the bonding in magnesium chloride showing all the outer electrons. [2] (ii) Write the equation for the reaction between sodium carbonate and magnesium chloride. [2] 11852 [Turn over (iii) Use the following headings to calculate the percentage of sodium carbonate in the salt sample. Relative formula mass of magnesium carbonate Number of moles of magnesium carbonate Number of moles of sodium carbonate Relative formula mass of sodium carbonate Mass of sodium carbonate in the sample Percentage of sodium carbonate in the sample [6]