Sodium metal and water react to form hydrogen and sodium hydroxide. if 17.94 g of sodium react with water to form 0.78 g of hydrogen and 31.20 g of sodium hydroxide, what mass of water was involved in the reaction

Astudent pours 10.0 g of salt into a container of water and observes the amount of time it takes for the salt to dissolve. she then repeats the process using the same amounts of salt and water but this time she slowly stirs the mixture while it is dissolving. the student performs the experiment one more time but this time she stirs the mixture rapidly. the dependent variable in this experiment is: time for salt to dissolve speed of stirring amount of water mass of salt