Here are the solutions to the questions: 19. A hydrocarbon containing $88.9\%$ carbon has the empirical formula [H=1, C=12]. Step 1: Determine the percentage of hydrogen. Since it's a hydrocarbon, it contains only carbon and hydrogen. $$ \% \text{H} = 100\% - \% \text{C} = 100\% - 88.9\% = 11.1\% $$ Step 2: Assume a $100\, \text{g}$ sample to convert percentages to masses. Mass of C = $88.9\, \text{g}$ Mass of H = $11.1\, \text{g}$ Step 3: Convert masses to moles using molar masses (C=12 g/mol, H=1 g/mol). Moles of C = $\frac{88.9\, \text{g}}{12\, \text{g/mol}} \approx 7.408\, \text{mol}$ Moles of H = $\frac{11.1\, \text{g}}{1\, \text{g/mol}} = 11.1\, \text{mol}$ Step 4: Find the simplest whole-number ratio by dividing by the smallest number of moles. Ratio of C:H = $\frac{7.408}{7.408} : \frac{11.1}{7.408} \approx 1 : 1.498$ Step 5: Multiply by a small integer to get whole numbers. Multiply by 2: Ratio of C:H = $1 \times 2 : 1.498 \times 2 \approx 2 : 2.996 \approx 2 : 3$ The empirical formula is C₂H₃. Answer: $\boxed{\text{c. C₂H₃}}$ 20. Which of the following methods can be used to separate blood cells from plasma? Explanation: Blood cells are suspended in plasma and are denser. Centrifugation* uses centrifugal force to separate components of different densities, making it ideal for separating blood cells from plasma. Answer: $\boxed{\text{a. centrifugation}}$ 21. The purity of a solid sample can best be determined by its... Explanation: The melting point* of a pure solid is a specific, sharp temperature. Impurities typically lower the melting point and broaden the melting range, making it a reliable indicator of purity. Answer: $\boxed{\text{b. melting point}}$ 22. The most suitable process of obtaining water from an acre solution of sugar is... Explanation: To obtain pure water from a sugar solution, the water needs to be separated from the dissolved, non-volatile sugar. Distillation* involves boiling the solution to vaporize the water, then condensing the vapor back into pure liquid water, leaving the sugar behind. Answer: $\boxed{\text{b. distillation}}$ 23. Potassium trioxonitrate(V) can be obtained from its solution by... Explanation: Potassium trioxonitrate(V) (KNO₃) is a soluble salt. To obtain the solid salt from its solution, crystallization* is the most suitable method. This involves evaporating the solvent until the solution is saturated, then cooling it to allow the salt to crystallize out. Answer: $\boxed{\text{c. crystallization}}$ 24. A mixture containing two salts of different solubilities can be separated by a. chromatography b. distillation c. crystallization d. evaporation Explanation: When two salts have different solubilities in a solvent, they can be separated by fractional crystallization*. This involves dissolving the mixture, then carefully changing conditions (e.g., cooling) to cause one salt to crystallize out before the other. Option c, crystallization, is the general principle. Answer: $\boxed{\text{c. crystallization}}$ 25. The separation technique that is suitable for separating iodine from tetrachloromethane is a. solvent extraction b. fractional distillation c. decantation d. filtration Explanation: Iodine is a solid that dissolves in tetrachloromethane (CCl₄), which is a liquid. To separate a dissolved solid from a liquid solvent, fractional distillation* is suitable. CCl₄ has a boiling point of $76.7\, \text{°C}$, while iodine sublimes at $113.7\, \text{°C}$ (and melts at the same temperature). The CCl₄ would distill off, leaving the solid iodine behind. Answer: $\boxed{\text{b. fractional distillation}}$ 26. When an ionic bond is broken, bonding electrons are... Explanation: An ionic bond forms when electrons are completely transferred from a metal (electropositive atom) to a non-metal (electronegative atom). When the bond breaks, the electrons remain with the atom that originally gained them, which is the most electronegative atom*. Answer: $\boxed{\text{c. gained by the most electronegative atom}}$ 27. The following molecules have double covalent bonds between two atoms except... Explanation: a. Oxygen (O₂): Has a double bond (O=O). b. Carbon(IV) oxide (CO₂): Has two double bonds (O=C=O). c. Ethene (C₂H₄): Has one double bond (H₂C=CH₂). d. Water (H₂O): Has two single bonds (H-O-H). Answer: $\boxed{\text{d. water}}$ 28. The formation of a bond between hydrogen and a highly electronegative atom results in a... Explanation: When hydrogen bonds with a highly electronegative atom (e.g., O, N, F), the electron pair in the bond is pulled more towards the electronegative atom. This creates an uneven distribution of charge, leading to a polar covalent bond. The property of having these separated partial charges is called polarity*. Answer: $\boxed{\text{a. polarity}}$ 29. The molecule that has a non-polar covalent bond is a. H₂O b. HCl c. NH₃ d. Cl₂ Explanation: A non-polar covalent bond forms between two atoms with identical or very similar electronegativity, resulting in equal sharing of electrons. a. H₂O: O-H bonds are polar. b. HCl: H-Cl bond is polar