Chemistry Questions & Answers

Determine whether an element is chemically reactive given only its electron configuration Explain how atoms of elements in Group 2 of the periodic table achieve a stable octet. "

Given chromium's electron configuration, \( 1 \mathrm{~s}^{2} 2 \mathrm{~s}^{2} 2 \mathrm{p}^{6} 3 \mathrm{~s}^{2} 3 \mathrm{p}^{6} 4 \mathrm{~s}^{2} 3 \mathrm{~d}^{4} \), what is the likely form of its ion?

- Explain how atoms of elements in Group 2 of the periodic table achieve a stable octet. *

a. What many elements are metals? b. How many elements are metalloids? c. How many elements are nonmetals? d. Does germanium have more in common with silicon or arsenic? Give the reason. e. Write down the name and chemical formula of the compound made of aluminum and phosphorus. [Hint: Aluminum and phosphorus are in groups \( 3 A \) and \( 5 A \), respectively.]

Explain the differences between a sodium ion and a sodium atom as well as the differences between a sodium ion and a neon atom. *

15. Write the chemical formulas or names of the following ionic compounds. (8pts) \( \begin{array}{ll}\text { a. barium fluoride } & \text { c. } \mathrm{Cu}_{2} \mathrm{O} \\ \text { b. mercury(II) phosphate } & \text { d. } \mathrm{Na}_{2} \mathrm{SO}_{4}\end{array} \) 16. Write the chemical formulas or names of the following molecular compounds. (8pts) \( \begin{array}{ll}\text { a. dichlorine heptoxide } & \text { c. } \mathrm{SF}_{6} \\ \text { b.chlorine dioxide } & \text { d. } \mathrm{N}_{2} \mathrm{O}\end{array} \)

Ten grams ( 10 g ) of an impure sample of sodium carbonate is added to \( 100 \mathrm{~cm}^{3} \) of a 0,2 mol \( \mathrm{dm}^{3} \) solution of hydrochloric acid. The acid is in excess. The equation for the reaction is: \( \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \) \( 8.3 .1 \quad \) Balance the equation above. \( 8.3 .2 \quad \) Calculate the number of moles of hydrochloric acid. The excess acid neutralises \( 20 \mathrm{~cm}^{3} \) of a solution of 0,1 mol.dm of magnesium hydroxide. \( 2 \mathrm{HCl}(\mathrm{aq})+\mathrm{Mg}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{MgCl}_{2} \) (aq) \( +\mathrm{H}_{2} \mathrm{O}(t) \)

Calcula la y en mol NaOH .61

8.2 Consider the following acid-base reaction: \[ \mathrm{H}_{2} \mathrm{PO}_{4}+\mathrm{NH}_{3} \rightarrow \mathrm{HPO}_{4}^{2}+\mathrm{NH}_{4}^{+} \] 8.2.1 Identify the conjugate acid-base pairs in the above reaction. 8.2.2 Define the term ampholyte. 8.2.3 Choose an ampholyte in the above reaction.

The atomic number of silver is 47 . How many neutrons are in a silver-108 atom? 155 47 61 108