To prepare a 1% barium chloride solution from a 99% stock solution, you need to know the desired volume of the final solution and the density of the barium chloride solution.

Let's assume the desired volume of the final solution is V (in liters). To prepare the 1% solution, you need 0.01 x V grams of barium chloride.

The mass of barium chloride in the stock solution is given by the density of the solution (ρ, in g/mL) multiplied by the volume (V, in mL):

Mass = ρ x V

So, to calculate the mass of barium chloride needed to prepare the final solution, we need to convert the desired volume of the solution to milliliters and multiply by the density of the barium chloride solution.

For example, if the desired volume of the final solution is 100 ml and the density of the barium chloride solution is 4 g/mL, the mass of barium chloride needed is:

Mass = 0.01 x 100 ml = 0.01 x 100 x 0.004 g/mL = 0.4 g

So, to prepare 100 ml of 1% barium chloride solution, you would need 0.4 g of barium chloride from the 99% stock solution.