A level chemistry

Sodium azide is toxic. It can be destroyed by reaction with an acidified solution of nitrous
acid (HNO2) as shown in the equation.
2NaN3 + 2HNO2 + 2HCl 3N2 + 2NO + 2NaCl + 2H2O
(i) A 500 cm3 volume of the nitrous acid solution was used to destroy completely 150 g
of the sodium azide.
Calculate the concentration, in mol dm−3, of the nitrous acid used


150 / 65 = 2.31 moles NaN3 or 2.31 moles nitrous acid
1
Conc = 2.31 ×
M2 is for M1 × 1000 / 500
1
4.6(1) or 4.6(2) (mol dm−3)
Only this answer

The markscheme says 1000/500 where did this come from?

Sodium azide is toxic. It can be destroyed by reaction with an acidified solution of nitrous
acid (HNO2) as shown in the equation.
2NaN3 + 2HNO2 + 2HCl 3N2 + 2NO + 2NaCl + 2H2O
(i) A 500 cm3 volume of the nitrous acid solution was used to destroy completely 150 g
of the sodium azide.
Calculate the concentration, in mol dm−3, of the nitrous acid used
150 / 65 = 2.31 moles NaN3 or 2.31 moles nitrous acid
1
Conc = 2.31 ×
M2 is for M1 × 1000 / 500
1
4.6(1) or 4.6(2) (mol dm−3)
Only this answer
The markscheme says 1000/500 where did this come from?

bro where does 1000/500 come from??