If a single 5-g block of NaCl is placed in water, it dissolves slowly, but if 5 g of powdered NaCl is placed in water, it dis- solves rapidly. Explain.

Video transcript

Hello. In this problem we are asked between a block of magnesium fluoride of a given mass and the same mass. A magnesium fluoride in the powder form, which will dissolve rapidly. So the rate of dissolution depends on the size of solid particle. And it also depends then on the number of collisions between the Sullivan and the saw you. The more collisions than the faster that the substance will dissolve. So when we think about then our block of magnesium chloride, right? We have this amount of surface over which then we can have collisions with water or another Sullivan. And if we have powdered and is employed, we have all this surface over which we can have interactions with our Sullivan. So here we have a large surface area as compared to our block which has a smaller surface area over which then collisions can take place between the solvent and the solid particles. This larger surface area then will lead to again an increased number of collisions between the solute and solvent. And this will then increase the rate of dissolution. So if we look at the answers we've been provided, it asks us the one that would dissolve more rapidly would be the block of magnesium fluoride. That's a we know that's not correct because it has a lower surface area. So lower area over which the Sullivan and Sullivan can interact. The powdered magnesium fluoride has a larger surface area. So we have a large number of collisions in between our salute and our Sullivan, which will then allow the magnesium quarry to go into solution faster. And he says that the rate would be the same. We've already eliminated A So that means then we eliminate C. So think about this. Also in terms of a sugar cube versus than a container or a packet of sugar, we know that it's going to take longer for a sugar cube to dissolve as compared to a packet of sugar. Thanks for watching. Hope this helps.