The chemistry of carbon dioxide and ocean water is, without writing a bunch of chemical formulas, something like this: carbon dioxide and water combine to form carbonic acid (H2CO3). It is a weak acid so it doesn't make the ocean super corrosive or anything. But it does shift a giant chemical equilibrium that exists in the ocean. The carbonic acid molecule is in equilibrium with bicarbonate ion (HCO3-) which is in turn in equilibrium with carbonate ion (CO3-2). That series of equilibria is called the "carbonate buffer system". The carbonate ions are in equilibrium with solid carbonate minerals - most notably limestone and coral, but also a good bit of Mollusca shells. As more carbon dioxide enters the ocean, it causes all the reactions to shift to undo the change caused by adding the carbon dioxide. So there are more bicarbonate ions and more carbonate ions in the ocean, and at each stage of the reaction shift, hydrogen ions are released and cause the pH of the ocean to drop.
In today's ocean almost all of the carbon in solution is in the form of bicarbonate ions. The equilibrium point for bicarbonate to be the preferred ion is just over a pH of 8. But as more hydrogen ions are produced and the pH shifts lower, the amount of bicarbonate is less and the amount of carbonic acid is greater. The carbonate buffer system resists changes to pH and in the ocean this happens by ocean water dissolving more carbonate minerals: as the carbon dioxide dissolves into the ocean from the atmosphere, the ocean in turn dissolves solid carbonates so the ocean pH doesn't change too much.
We'd be perfectly content if the ocean simply dissolve a bunch of limestone and the carbon dioxide stayed dissolved in the ocean forever. But the ocean has much better contact with the shells of those Mollusca and the coral reefs than it does with limestone rocks, so the shells and reefs tend to dissolve first. The mollusks and the reefs are the basis of much of the ocean food chain. Acidifying the ocean with carbon dioxide is a really bad idea.
But there is lots of limestone around. Maybe we could just react carbon dioxide directly with the limestone and leave the mollusks and corals out of it? That is the basis of acid scrubbers on fossil fuel power plant stacks. The scrubber is a tank full of crushed limestone with water trickling over it and the gases go through. The acidic stuff in the gas dissolves in the water and the acidified water dissolves some of the limestone. Instead of calcium carbonate rock, it becomes calcium bicarbonate solution. Sadly, when one tries to dry out the solid calcium bicarbonate, it perversely gives up a carbon dioxide molecule and turns back into calcium carbonate.
This feature of carbon dioxide stubbornly reappearing is common to various scrubbing technologies: the carbon dioxide is captured but it remains as carbon dioxide. It is a quite energetically stable molecule so it does not have a lot of beneficial above-ground chemical industrial sorts of uses (basically, none). If we are not allowed to vent it into the atmosphere, what are we to do with it? The most common solution appears to derive from the concept that it came out of the ground, so let's put it back. Carbon dioxide can be injected into the ground where it will stay for a long time. The oil industry volunteers that they can use it to extract more oil! They are not helping.
I think back in the ground is the best solution for now. Maybe in the future we will be able to do like plants and convert carbon dioxide and water and sunlight into cellulose. We can't do that yet except by planting more trees.