OAT General Chemistry - Problem Drill 04: Writing Formulas Question No. 1 of 10 1. Which of the following is correct for sodium oxide? Question #01 (A) SO (B) S 2 O (C) NaO (D) Na 2 O (E) NaO 2 Sodium is symbolized with Na. Sodium is symbolized with Na. These are the correct symbols, but the charges must be balanced. D. Correct! The charges are balanced in this formula. E. Incorrect! You have the right elements, but not the subscripts. The charges must be balanced. This is binary ionic compound. Sodium is Na +1 Oxide is O -2 Na +1 Na +1 O -2 would give a neutral compound. Answer: (D) Na 2 O
Question No. 2 of 10 needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 2. Which of the following is the correct formula for carbonous acid? Question #02 (A) HCO 3 (B) H 2 CO 3 (C) HCO 2 (D) H 2 CO 2 (E) HCO ous acids came from ite anions. ous acids came from ite anions. Remember to balance the charges. D. Correct. The charges are balanced in this formula. The charges are not balanced in this neutral compound. This is an acid. -ous acids came from -ite polyatomic ions. Carbonite is CO 2-2 Acids begin with H +1 H +1 H +1 CO 2-2 would give a neutral compound. Answer: (D) H 2 CO 2
Question No. 3 of 10 needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 3. Which of the following is correct for Ammonium phosphate? Question #03 (A) NH 4 PO 4 (B) (NH 4 ) 3 PO 4 (C) NH 4 (PO 4 ) 3 (D) (NH 4 ) 12 PO 4 (E) (NH 4 ) 4 PO 4 You need to balance the charges. B. Correct! The charges are balanced. The charges aren t balanced. Don t multiple the charge by a subscript within the polyatomic ion. Check the charges of both the anion and cation. They must be balanced. This is a polyatomic ionic compound. Ammonium is NH 4 +1 Phosphate is PO 4-3. You do not multiply the polyatomic ion s subscripts by its charge. NH 4 +1 NH 4 +1 NH 4 +1 PO 4-3 would give a neutral compound. Answer: (B) (NH 4 ) 3 PO 4
Question No. 4 of 10 needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 4. Which of the following is correct for Copper (II) hydroxide? Question #04 (A) Cu 2 OH (B) CuOH 2 (C) Cu(OH) 2 (D) Co 2 OH (E) CuOH The Roman numeral II doesn t mean two atoms, it means a charge of +2. When using a subscript with a polyatomic ion, make sure to use parenthesis. C. Correct. The charges are correctly balanced. The symbol for copper is Cu. The charges are not balanced in this formula. This is a polyatomic ionic compound. The roman numeral gives the cation charge. Copper (II) is Cu +2 Hydroxide is OH -1. Cu +2 OH -1 OH -1 would give a neutral compound. Remember to use parenthesis with polyatomic ions. Answer: (C) Cu(OH) 2
Question No. 5 of 10 needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed. 5. Which of the following is correct for silicon dioxide? Question #05 (A) SiO 2 (B) Si 2 O (C) SiO (D) SO 2 (E) SiO 4 A. Correct. The Di indicates there are two oxygen atoms. The Di is with the oxygen, not the silicon. Di means two oxygen atoms, not one. The symbol for silicon is Si Di means two oxygen atoms, not four. This is a binary covalent compound. Do not worry about charges as they don t form charges just write what the compound says, using prefixes to designate subscripts. (Remember mono is not used on the first element). Silicon is Si. Dioxide is O 2. Answer: (A) SiO 2
Question No. 6 of 10 6. Which of the following is correct for iron (III) carbonate? Question #06 (A) Fe 3 CO 3 (B) Fe 3 (CO 3 ) 2 (C) Fe 2 (CO 3 ) 3 (D) Fe 2 CO 3 (E) FeCO 3 The Roman numeral III indicates a +3 charge, not 3 atoms. The Roman numeral III indicates a +3 charge, not 3 atoms. C. Correct. The charges are correctly balanced. You need to balance the charges. You need to balance the charges. This is a polyatomic ionic compound. The roman numerals give the charge of the cation. Iron (III) is Fe +3 Carbonate is CO 3-2 Fe +3 Fe +3 CO 3-2 CO 3-2 CO 3-2 is a neutral compound. Answer: (C) Fe 2 (CO 3 ) 3
Question No. 7 of 10 7. Which of the following is hydrosulfuric acid? Question #07 (A) HS (B) H 2 S (C) H 2 SO 3 (D) H 2 SO 4 (E) H 2 SO 2 You need to balance the charges. B. Correct! A hydro acid does not contain oxygen and the charges are balanced. A hydro acid does not contain oxygen. A hydro acid does not contain oxygen. A hydro acid does not contain oxygen. hydro acids do not contain oxygen. sulfuric is S -2 Acids begin with H +1 H +1 H +1 S -2 is a neutral compound. Answer: (B) H 2 S
Question No. 8 of 10 8. Which of the following is dinitrogen tetraoxide? Question #08 (A) Ni 2 O 4 (B) N 2 O 4 (C) Ni 2 O 3 (D) N 2 O 3 (E) NO The symbol for nitrogen is N. B. Correct. The di and tetra indicate how many atoms are in the molecule. The symbol for nitrogen is N. tetra stands for 4 atoms of oxygen. Hint: The di and tetra indicate how many atoms are in the molecule. This is a binary covalent compound. They do not form charges. Use the prefixes to indicate subscripts. Dinitrogen is N 2 Tetraoxide is O 4 Answer: (B) Ni 2 O 4
Question No. 9 of 10 9. Which of the following is calcium fluoride? Question #09 (A) Ca 2 F (B) CaF (C) CaF 2 (D) CF 2 (E) Ca 2 F 2 The charges aren t balanced. The charges aren t balanced. C. Correct. The +2 charge of the calcium ion is balanced with 2 fluoride ions with -1 charge each. The symbol for calcium is Ca. The charges aren t balanced. This is a binary ionic compound. Calcium is Ca +2 Fluoride is F -1 Ca +2 F -1 F -1 is a neutral compound. Answer: (C) CaF 2
Question No. 10 of 10 10. Which of the following is phosphoric acid? Question #10 (A) HP (B) H 3 P (C) H 3 PO 4 (D) H 12 PO 4 (E) H 3 PO 3 Acids without hydro contain oxygen. Acids without hydro contain oxygen. C. Correct. The ic acid came from the ate anion. Don t multiply the charge of a polyatomic ion by the subscript within the ion. The ic acid came from the ate anion. Phosphate is PO 4-3. This is an acid. -ic acids come from -ate polyatomic ions. Phosphate is PO 4-3 Acids begins with H +1 H +1 H +1 H +1 PO 4-3 is a neutral compound. Answer: (C) H 3 PO 4