Chemistry questions and solutions
Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.
364 questions · Page 16 of 16
- Q152 · Original practice · 5 marksOrganic analysisThree amino acids are placed at the origin in separate lanes for electrophoresis in a buffer of pH 6.0. The positive electrode is on the left and the negative electrode is on the right. Use the pI values in the table. Ignore bulk movement of the buffer.
- Q153 · Original practice · 5 marksOrganic analysisAn amino-acid mixture is compared with three standards by TLC in two different solvent systems. In system 1 the solvent front travels 8.0 cm; the mixture has spots at 2.4 cm and 5.6 cm. In system 2 the mixture has Rf values 0.50 and 0.60. All standard comparisons are made under the same conditions within each solvent system.
- Q154 · Original practice · 4 marksOrganic analysisThe simplified mass spectrum is from one of these compounds: ethanol, ethane, chloroethane or 1-chloropropane. Its molecular-ion pair is at m/z = 64 and 66. Chlorine has isotopes with masses 35 and 37 in an approximate 3:1 abundance ratio. Use C = 12, H = 1 and O = 16. The infrared spectrum has no O–H absorption.
- Q155 · Original practice · 8 marksChemical synthesisAn ethanol plant compares two routes. Route F ferments 90.0 g of glucose at 80.0% ethanol yield, then recovers 90.0% of the ethanol formed. Route H hydrates 1.50 mol of ethene at 60.0% ethanol yield, then recovers 95.0% of the ethanol formed. Water is in excess. The fermentation enzymes lose catalytic activity when heated far above their operating range. Use…