Jade wants to measure the thickness of a copper wire. She wound the copper wire 30 times around a pencil and used a ruler to measure the length of the wound wire as shown in the figure. Section of ruler is shown next to a pencil with a wire wound around it. The markings on the ruler are from zero to two centimeters. There are two small markings, one is between zero and one and the other is between one and two. The length of the entire wound wire starts at zero and goes to the small marking which is exactly between one and two. Which of these is the most accurate thickness of the copper wire?

1) 36.70 %; 2) 39.05 %; 3)17.75 %

Step-by-step explanation:

% of element = Mass of element/mass of compound × 100 %

1) N in Mg(CN)₂

The masses of each element are:

1Mg  = 1  × 24.30 = 24.30 u

2C    = 2 × 12.01  = 24.02 u

2N    = 2 × 14.01  = 28.02 u

              TOTAL = 76.34  u

% N = 28.02/76.34 × 100 %

      = 36.70 %

2) K in KHCO₃

The masses of each element are:

1K  = 1 × 39.10    =   39.10   u

1H = 1 ×     1.008 =     1.008 u

1C = 1 ×  12.01     =     2.01   u

3O = 3 ×  16.00   = 48.00   u

           TOTAL    = 100.12    u

% N = 39.10/100.12 × 100 %

      = 39.05 %

3) H in NH₃

The masses of each element are:

1N  = 1 × 14.01   = 14.01   u

3H = 3 ×    1.008 =   3.024 u

                TOTAL   = 17.03   u

% N = 3.024/17.03 × 100 %

        = 17.75 %