Which of the following is not an example of a chemical change?

digesting food
burning gas in an engine
cooking eggs
grinding pepper

The rock in a lead ore deposit contains 89 % pbs by mass. how many kilograms of the rock must be processed to obtain 1.5 kg of pb?

Calculate the expected ph values of the buffer systems from the experiments (a,b,c,d), using the henderson- hasselbalch equation, ph-pka+log[a-]/[ha]. use for pka values carbonic acid= 6.37, and acetic acid= 4.75.

Calculate the mass of carbon in 97.0 g of sucrose c12h22o11