Solid calcium carbonate

A carbonated slurry of cyanamide solution, solid calcium carbonate, and graphite is cooled to remove the heat of reaction. Part of the slurry is recycled to faciUtate temperature control whereas the remainder is filtered yielding cyanamide solution and a cake of calcium carbonate and graphite. The filtered solution is also recycled ia order to control the soHds content. The final concentration of cyanamide is normally maintained at 25%. 

Oceanic surface water is everywhere supersaturated with respect to the two solid calcium carbonate species calcite and aragonite. Nevertheless carbonate precipitation is exclusively controlled by biological processes, specifically... 

Inside newiy formed caverns, calcium carbonate precipitates from water dripping from the ceilings of the chambers. This happens when water that is saturated with carbon dioxide and calcium hydrogen carbonate comes into contact with air. Some of the dissolved CO2 escapes into the gas phase. This shifts the two equilibria to the left, and solid calcium carbonate precipitates ... 

The major species present initially, other than water, are solid calcium carbonate and aqueous hydronium ions. 

Hydroiodic acid is mixed with solid calcium carbonate. 

Solid calcium carbonate decomposes to produce solid calcium oxide and carbon dioxide gas. The value of AG° for this reaction is 130.24 kJ/mole. Calculate AG at 100°C for this reaction if the pressure of the carbon dioxide gas is 1.00 atm. 

Solid calcium carbonate decomposes into solid calcium oxide and carbon dioxide gas. 

Thus far we ve been discussing homogeneous equilibria, in which all reactants and products are in a single phase, usually either gaseous or solution. Heterogeneous equilibria, by contrast, are those in which reactants and products are present in more than one phase. Take, for example, the thermal decomposition of solid calcium carbonate, a reaction used in manufacturing cement ... 

When the reaction is carried out in a closed container, three phases are present at equilibrium solid calcium carbonate, solid calcium oxide, and gaseous carbon dioxide. If we were to write the usual equilibrium equation for the reaction, including all the reactants and products, we would have... 

Sample A piece of solid calcium carbonate is added to a solution of dilute hydrochloric acid. 

A standard solution of 0.250 mol/L calcium ion is prepared by dissolving solid calcium carbonate in an acid. What mass of calcium carbonate is needed to prepare 1.00 L of the solution ... 

Note that the solubility product constant expression is true only when there is undissolved, solid material still present in the system. In other words, we are talking about (in this case) solid calcium carbonate in equilibrium with a saturated solution of calcium carbonate. 

It is important to remember that this last calculation assumed that solid calcium carbonate was present in the system for example, the lake bed was limestone. It should be clear that the partial pressure of CO2 over a lake cannot usually exceed about 380 ppm, the global average atmospheric concentration, and thus, the calcium concentration cannot exceed a certain level if that partial pressure is to be maintained. In the above calculation, remember that the exponent —11.24 was based on a C02 partial pressure of 380 ppm. At this pressure and at a pH of 8.23 (which is what we just calculated), the calcium concentration is given by... 

In other words, at 380 ppm of C02, the maximum dissolved calcium concentration is about 500 pM. Of course, it can be less if all of the solid calcium carbonate is dissolved, and it can be more if the pressure of C02 is higher (as it might be in a groundwater sample or in a closed can of a carbonated beverage). Let us ask a more general question. 

Consider a vessel containing solid calcium carbonate, CaCOs. When heated, the carbonate decomposes into lime (solid calcium oxide), CaO, and gaseous carbon dioxide, CO2. Experimentally, the concentration of CO2 is found to be constant at a definite temperature and, therefore, independent of the amounts of the other phases. Describe the type of system and equilibrium. 

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of... 

In some cases, the net ionic eqnation is significantly simpler than the full equation. For example, consider the reaction of solid calcium carbonate with a limited quantity of hydrochloric acid. (In this case, these substances react in a 1 1 ratio.) Assuming that the chloride ion is a spectator ion allows us to write the net ionic equation direcdy ... 

This reaction, however, also increases the concentration of carbonate ions, causing solid calcium carbonate to form. This solid is the boiler scale that coats the walls of containers such as industrial boilers and tea kettles. Boiler scale reduces the efficiency of heat transfer and can lead to blockage of pipes (see Fig. 17.7). 

Limestone (calcium carbonate) particles are stored in 50-L bags. The void fraction of the particulate matter is 0.30 (liter of void space per liter of total volume) and the specific gravity of solid calcium carbonate is 2.93. 

An aqueous waste stream leaving a process contains 10.0 wt% sulfuric acid and 1 kg nitric acid per kg sulfuric acid. The flow rate of sulfuric acid in the waste stream is 1000 kg/h. The acids are neutralized before being sent to a wastewater treatment facility by combining the waste stream with an aqueous slurry of solid calcium carbonate that contains 2 kg of recycled liquid per kg solid calcium carbonate. (The source of the recycled liquid will be given later in the process description.)... 

The slurry leaving the crystallizer is filtered to produce (i) a filter cake containing 96% calcium sulfate crystals and the remainder entrained saturated calcium sulfate solution, and (ii) a filtrate solution saturated with CaS04 at 30 C that also contains dissolved calcium nitrate. The filtrate is split, with a portion being recycled to mix with the solid calcium carbonate to form the slurry fed to the reactor, and the remainder being sent to the wastewater treatment facility. 

TEST 1. Estimate the heat capacity of solid calcium carbonate (CaCOr) using Kopp s rule and... 

A system formed of calcium carbonate, of lime, and of carbonic acid gas has three phases solid calcium carbonate, solid lime, carbonic acid gas. 

Limestone caverns, shown in Figure 6, form over millions of years. They are made as rainwater, slightly acidified by HsO", gradually dissolves rocks made of calcium carbonate. This reaction is still going today and is slowly enlarging caverns. The reverse reaction also takes place, and solid calcium carbonate is deposited as beautiful stalactites and stalagmites. 

Available forms Calcium chloride in hydrochloric acid solution and solid calcium carbonate. 

When an acid—for example, hydrochloric acid—is added to solid calcium carbonate, a reaction occurs in which carbonic acid, a weak acid, is produced. 

Oceanic surface water is everywhere supersaturated with respect to the two solid calcium carbonate species calcite and aragonite. Nevertheless, calcium precipitation is exclusively controlled by biological processes, specifically the formation of hard parts (shells, skeletal parts, etc.). The very few existing amounts of spontaneous inorganic precipitation of CaC03(s) come from the Bahamas region of the Caribbean. 

Problem 8 Solid calcium carbonate (CaC03) exposed to intense heat forms calcium oxide (CaO) and carbon dioxide (C02), until this equilibrium is reached ... 

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