Bacteria in water samples are sometimes difficult to count, but their presence can simply be detected by culturing. In 50 independently selected water samples from the certain lake, 43 contained certain harmful bacteria. After adding chemical to the lake water, another 50 samples showed only 22 with harmful bacteria. Determine the true difference between proportions of samples containing the harmful bacteria, with the 95% confidence coefficient. Does the chemical appear to be effective in reducing amount of bacteria?