Final answer:
When rubidium ions are heated to a high temperature, they emit two lines in their line spectrum. The frequencies of these lines are approximately 3.80 × 10^14 Hz and 7.14 × 10^14 Hz. Therefore, the color we see when we heat a rubidium compound is violet.
Step-by-step explanation:
When rubidium ions are heated to a high temperature, two lines are observed in its line spectrum at wavelengths (a) 7.9 × 10-7 m and (b) 4.2 × 10-7 m. To find the frequencies of the two lines, we can use the formula c = λf, where c is the speed of light. Rearranging the formula, we have f = c/λ. Plugging in the values, we get:
(a) f = 3.00 × 108 m/s ÷ 7.9 × 10-7 m = 3.80 × 1014 Hz
(b) f = 3.00 × 108 m/s ÷ 4.2 × 10-7 m = 7.14 × 1014 Hz
To determine the color we see when we heat a rubidium compound, we look at the frequency of the light. From the frequencies we calculated earlier, we can see that (a) corresponds to a frequency of 3.80 × 1014 Hz, and (b) corresponds to a frequency of 7.14 × 1014 Hz. Since violet light has a frequency range of approximately 7.5 × 1014 to 5 × 1014 Hz, we can conclude that the color of the emitted light when we heat a rubidium compound is violet.