Coltan

COLTAN, MINERAL DE GUERRA

Cambios de estado de agregación

Changing States of Matter

All matter can move from one state to another. It may require extreme temperatures or extreme pressures, but it can be done. Sometimes a substance doesn't want to change states. You have to use all of your tricks when that happens. To create a solid, you might have to decrease the temperature by a huge amount and then add pressure. Some of you know about liquid nitrogen (N₂). It is nitrogen from the atmosphere in a liquid form and it has to be super cold to stay a liquid. What if you wanted to turn it into a solid but couldn't make it cold enough? You could increase the pressure to push those molecules together. The opposite works too. If you have a liquid at room temperature and you wanted a gas you could use a combination of high temperatures and low pressures to solve your problem.

Phase changes happen when certain points are reached. Sometimes a liquid wants to become a solid. Scientists use something called a freezing point to measure the temperature at which a liquid turns into a solid. There are physical effects that can change the freezing point. Pressure is one of those effects. When the pressure surrounding a substance goes up, the freezing point and other special points also go up. That means it's easier to keep things solid at higher pressures. Just remember that there are some exceptions. Water (H₂O) is special on many levels. It has more space between its molecules when it is frozen. There's a whole expanding effect when the molecules organize into a solid state. Generally, when temperatures get colder, solids shrink in size. They become more dense.

CHEMISTRY TERM	PHASE CHANGE
Fusion (melting) Freezing Vaporization (boiling) Condensation Sublimation Deposition	Solid to Liquid Liquid to Solid Liquid to Gas Gas to Liquid Solid to Gas Gas to Solid

Esquema cambios de estado de la materia

Algunos cambios de estado

¿Se deben evitar los nitratos y nitritos en los alimentos?

AVOID NITRATES AND 

NITRITES IN FOOD

April 1, 2013

Nitrates and nitrites are chemical compounds that cause a lot of consumer confusion.

Nitrates are a normal part of the diet, but excessive levels can cause problems, especially for kids who pound for pound take in more than adults do. They have been linked to diseases like leukemia, non-Hodgkin lymphoma, and ovarian, colon, rectal, bladder, stomach, esophageal, pancreatic, and thyroid cancer.

They’re found in our diets in several ways: as synthetic food preservatives and naturally occurring in fruits and vegetables like spinach and celery. Sodium nitrate and potassium nitrite are added to cured meat to preserve its color, prevent fats from going rancid, and stop bacteria from growing. They’re also found in drinking water thanks to nitrogen-based fertilizers as well as livestock waste.

Here’s where things get tricky: If nitrites are exposed to high heat during cooking, they can convert to nitrosamines, which are carcinogenic. And when nitrates are used as a food additive or consumed, they can convert into nitrites.

Scientists believe that these conversions may be responsible for the link they’ve discovered between nitrates and nitrites and the diseases listed above. Nitrate or nitrite exposure has also been known to cause pregnancy complications and infant health problems.

Before you give up celery for good, keep in mind that there’s a difference between eating nitrates added to foods as preservatives and consuming them via produce. Nitrates that occur naturally are found alongside compounds like vitamin C that inhibit their conversion into nitrosamines in the body. When we eat nitrates and nitrites in foods artificially treated with them, we may not be getting these complementary nutrients and their preventative effects.

Here’s how to keep nitrates and nitrites off your plate:

1. Minimize consumption of processed foods and cured meat products like hot dogs, sausage, and cold cuts. Check labels carefully though—these compounds are also found in other products that contain processed meat and even some meat-free products.

2. Don’t be fooled by “uncured” or nitrate-free brands. These products typically contain high amounts of nitrates obtained from ingredients like celery juice, which means they could contain as much as if not more than their traditional counterparts.

3. Eat organic foods. They’re not grown with synthetic nitrogen fertilizers, which can boost a crop’s nitrate content significantly.

4. If you live in an agricultural region, consider treating your water with a home water distiller, a reverse osmosis filter, or an ion exchange filter to remove any fertilizer nitrates that have accumulated in the groundwater.

5. Eat a diet high in antioxidants. Certain vitamins, like vitamin C, can reduce the conversion of nitrates.

http://healthychild.org/easy-steps/avoid-nitrates-and-nitrites-in-food/

Organizador gráfico sobre nitratos y nitritos en los alimentos

KNOW	WANT TO KNOW	LEARNED
- El consumo de nitratos y nitritos en la dieta debe ser el menor posible ya que son cancerígenos. - Estos compuestos se encuentran en los conservantes y colorantes utilizados en la elaboración de fiambres, panchos, chorizos, etc.	- ¿Qué cantidad de nitratos y nitritos es recomendable consumir para que no tengan efectos adversos en la salud?  - ¿Qué otros efectos puede tener para el organismo? - ¿En qué otros alimentos, además de carnes procesadas, se encuentran estos compuestos? - ¿Existen alimentos que “neutralicen” su efecto? -  Si son cancerígenos, ¿por qué se permite su uso en este tipo de alimentos que muchas personas consumen a diario?	- Los nitratos son una parte normal de la dieta, peo niveles excesivos pueden causar problemas. - Su consumo se ha relacionado con enfermedades como leucemia, linfoma no- Hodking, de ovario, colon, recto, vejiga, estómago esófago, páncreas y cáncer de tiroides. También se sabe que causan complicaciones en el embarazo y problemas de salud infantil. - Además de hallarse como conservante se encuentran en algunas frutas y verduras, y en el agua potable como consecuencia de los fertilizantes a base de nitrógeno y los residuos ganaderos. - Su consumo en frutas y verduras no es riesgoso pues se encuentran junto a la vitamina C que inhiben su conversión en nitrosminas en el cuerpo. Para minimizar los efectos negativo de estos compuestos se aconseja: minimizar el consumo de alimentos procesados y productos cárnicos curados, consumir alimentos orgánicos, considerar el tratamiento de agua con un destilador en el hogar, y tener una dieta rica en antioxidantes.

Alimentos que contienen nitratos y nitritos